The Solo Mini is a scaled down version of the Solo. It's less powerful, but qualitywise basically the same. Some may feel the SOlo sounds better because of the extra power, giving it a more authoritive sound. The Solo can certainly drive some awkward speaker loads, and I've used it with some speakers in the past that I would never have normally dreamed of putting on the end of a mini system
Wow, I usually get moaned at for "guessing" what stuff sounds like! It's really down to the difference between Arcam and Naim. Arcam is generally a more laid back, smoother sound that many find they can easily listen to for a longer period of time. This sort of presentation helps with 'sharper' sounding loudspeakers. Naim is a little more 'up front', with a leaner, but still fairly warm sounding bass when partnered with the right speakers. If you want to get an idea between the two now, just pop into a local dealer and have a listen to either a Solo vs Uniti, or if one of the two aren't available, even a Nait 5i/CD5i vs FMJ A28/CD17 will show you the different ideas each manufacturer has about audio.