I can see the logic to thinking spending £100 on speakers on a £180 system doesn't make sense.
However things are not as straight forward as it would seem.
Yes the system may only cost £180, but its performance far outweighs its price.
You really need to spend far more money on the "system" to get much more improvement in sound.
Not so with the speakers.
A £60 set of speakers can be bettered by a £120 set of speakers by some margin. (so you are only spending an extra £40-£60)
(Having said that, choosing the "wrong" speaker even if it costs more doesn't guarantee a better sound!)
You will normally find the frequency response is wider, and the speaker to be more dynamic.
Depending on which speaker you buy, you should also notice less compression and extra depth and clarity.
The better speaker should also have less colouration and a better quality crossover circuit.
Believe me, i'm not one for spending money on anything that i don't see improvement on.
I pass on "expensive" speaker cables, as i don't see (hear) any "improvement".
Chunky oxygen free cable is my limit, and that only costs a couple of quid a metre.
Shielded power leads also get the push, as i just cannot see/hear ANY difference. (even on VERY high end equipment)
I did make sure my speaker stands were weighty(sand filled), but again they didn't cost much either.
Blu-tak secures the speakers to the stands, as i don't see any reason spending more on anything else.
I find speaker positioning and room objects to have a bigger influence on the overall sound. (ie get the room right and good sound will follow)
I've listened to many speakers around the £50 - £250 mark, and there can be a dramatic difference to the sound.
Some are bright, others bassy. Some seem muddled, whilst other have great clarity.
Listen to any mini systems that price varies by £200 on the same set of speakers and the differences will be much smaller.
So yes the DM37 may only cost a couple of hundred quid, but choose the right speaker for your tastes, and you will get even better performance.
I went for a set of Tannoy F2s at £80 (price varies from £80-£120), and they are a good match for the Denon and my tastes.
What suits me may not suit everybody though.
But one thing you cannot deny about the Tannoys is that frequency response is good and the clarity second to none in that price range.
My previous "Missions" sounded compressed compared to these speakers.
If you don't hear much difference between the standard (supplied) speakers and other aftermarket speakers, then i wouldn't worry about it.
It not about having "better" speakers, it's about having the best sound that suits you.
If the supplied speakers are good enough, then spending even one pound on anything else would be a waste...