If you're not using them with a sub, they'd have to go right against a wall to boost their bass output. Even so, they will still lack extension. Ideally you'll need a sub to complete things, but if you don't mind the sound being a little 'lightweight', especially at lower volumes, you should be ok.
If you're not listening at high levels, you could add a notch or two to the bass just to warm things up a little.
Yep, as Helicon says, they're a little lightweight in the bass department, but they're still enjoyable. I use mine with an MF X-Ray v3 / MF X-150 combo and it's a nice sounding combination, but not really comparable to a full-sized box for the lower notes. In this configuration, I can't use a sub either. If I want bass, I let my AV receiver to the work, but a lot of detail and resolution is lost this way.
As far as hooking them up to a mini-system goes, though, I have no idea. Guess it depends on the power of the system. They're not particularly hard to drive, but I think they might be a little wasted on a mini-system. That said, if you're picking them up for a good price, it's likely to be a good improvement on the standard speakers that came with the system.
Thanks for the replies - it was just a thought. I was going to get a proper hifi system, and it would have been the MF system quoted by doctorjuggles above, but with MA GS20s. (I had a demo of this and it was very very good). However, I since thought that such a system would be a waste as I rarely listen to music, and I'm now quite taken with my AV system's musical abilities. I have M&K LCR 850s with an M&K VX860 sub. My amp is a Rotel RSX 1067. I intend to get the next version of the Denon A11 XVA, when it comes out, as an upgrade to the Rotel (I had a Denon A11SR before the Rotel), so a full blown stereo system is not required. I would, however, like an inexpensive hifi setup, with floor standing speakers for occasional use, hence the system mooted in my original post.
How about just running a pair of speakers off the 2nd zone of the Denon? The MA's will only need a little sub to fill in, a Rel Quake will do the job fine. I'm sure one could be picked up used for not too much pocket money.