It really depends on what you want to achieve and what you currently find lacking.
For example do you find it annoying to have to have your phone connected while streaming? Are you looking for a better app/interface than Apple Music? Are you looking for management of a local music library of ripped CDs or downloaded FLAC files. Or are you just assuming that because your Marantz is a bit old you might be able to get better sound nowadays?
Starting with that last one, if you're keeping the Marantz and are happy with everything else then honestly I doubt you'll see much improvement by adding an external DAC. Sure different DACs can have slightly different sound signatures and if you're switching back and forth you might notice a small difference. Better or worse, that's hard to say. DAC chips (a few dollars a piece) have long reached the point that there isn't much in them, all can handle the D2A conversion with ease. In the grand scheme of things your room and speakers will have
by far the bigger effect on your overall sound, followed by the preamp stage in your AVR or Amp, by the point you get to the DAC chip you're effectively rearranging deckchairs. Also if you're using the sub output then the analog input will probably be sent though the Marantz's DAC anyway in order to handle the electronic crossover, rendering it a pointless upgrade.
If you're finding it annoying to have to have your phone connected while streaming, then you may find that using the HEOS app or a 3rd party DLNA supporting app like mConnect or BubbleUPnP with your Marantz rather than Apple Music via AirPlay offers some advantages, as once you start playback the Marantz will stream directly from your streaming service, rather than being routed via AirPlay from your phone. This means you can start a playlist and then switch your phone off or use it for other purposes without interfering with whatever you're streaming.
There could be real benefit here, the catch is none of those apps work with Apple Music and even if they did you may still prefer to keep using the Apple Music app over the streamers own app anyway. Although nothing stopping you trying them out with say Qobuz to see if it works for you.
Sorry, at this point your probably thinking "But I just want to buy a new toy...don't tell me none of them will make any difference" ;-)
If you like the idea of being able to take your phone out of the loop and use it for other audio tasks while streaming, but don't like the HEOS app or the functionality/interfaces provided by the freely available DLNA apps like mConnect or BubbleUPnP. Or you find that the lack of decent desktop DLNA apps frustrating. Then a streamer like the BlueSound, which has both a pretty well designed mobile and desktop app might be something that's worth paying for. This will work for Qobuz/Tidal/Deezer but for Apple Music you'll still be using AirPlay and the Apple Music App (as BlueOS has no direct integration with Apple) so you'll still need to keep your phone or Mac/PC tied up while streaming.
Unless something has changed since I last looked the Arcam MusicLife app and the Cambridge Audio StreamMagic app seem to be little more than rebadged/white label 3rd party control apps ie. they don't offer much in terms of features or interface design above the mConnect or BubbleUPnP apps and I expect we're largely outsourced. Whereas NAD (BlueSound) and Sonos seem to have invested more heavily in their own in-house software development teams which manifests itself in their better designed apps and interfaces.
In fact most of the traditional HiFi vendors seems to be moving away from any serious effort to develop their own apps in-house (unsurprising given that software development is costly) and instead are just relying on the streaming services native apps (Tidal Connect/Spotify Connect) or acting as an AirPlay, DLNA or Roon (
RAAT) endpoint. In which case you're possibly paying a lot of money for very little functionality, especially if you're not even using the DAC or PreAmp sections in the streamer and simply using it as a digital transport — as long as they support the same protocols and aren't screwing anything up, digital transport X should perform exactly the same as digital transport Y in terms of sound quality.
--
Roon is an interesting one and kind of hard to succinctly describe (why it's good). It's less of a proposition if you don't have a local music library and you're only using it with one audio setup. As local library management and (vendor neutral) muti-room audio are two of it's killer features.
But even if your not using those features it does offer something that most of the hardware based products don't, which is it's
fantastic control apps (I haven't used anything that is as good),
enhanced metadata (Roon pulls in a huge amount of extra information for every album, artists and genre in your library) and
discovery tools (which recommend new music to you in clever ways based on your listening history that isn't influenced by the record companies or streaming platforms). It's also got a fairly comprehensive
DSP engine if that's something that interests you. Think of it as the gold standard/grand daddy of library management and music control apps.
I think Roon probably appeals most if you're the sort of person who likes to read up on what you're listening to, or go on little journeys jumping from one artist to another and discovering or rediscovering music along the way. If you're the sort of person who plays the same two dozen albums over and over again or knows exactly what they want to listen to it adds little value. It also has a strong concept of a 'local library' allowing you to cherry pick albums from the streaming services vast catalogs to build a smaller (more manageable) local library.
The nice thing is you can try Roon out on your Mac or PC for free (you need to hand over your credit card to start the trail, but you can easily cancel before the 30 days is up).
To properly use Roon you ideally want to give it it's own server which is switched on 24/7, so that your Mac/PC isn't tied up and there's a whole world of options there from
DIY ROCK servers, to
Roon on a NAS, to Roon's own commercial
Nucleus device. But they all use the same control apps, so you can get a feel for how Roon and the Roon control apps work before going any further. In fact if your happy leaving your PC/Mac on 24/7 then you can just leave the Roon Core running on it in the background, and use the mobile/tablet apps to control playback instead.
Anyway, hope that is all of some help..
