I bought the Mini Utopias after well over a year of listening to every kind of speaker I could. For overall transparency and naturalness, I think it's up with the best there is. And the tweeter, which is the same as in the Utopia and Grand Utopia, is the best there is, period.
The bass rolls off gracefully at about 50 Hz., which is the speaker's real limitation. Everything else is so tremendous about this speaker that many people will say "Who care's about those last 30 Hz?!" But if you're a real bass lover, there are several options to consider.
1. The Utopia Sub II does make a perfect match. The downside is that it's so expensive.
2. For not all that much more than the Minis and the Utopia Sub, you can get the floorstanding JM Lab Mezzo Utopias, which sound even better than the Minis plus the sub. The downside, for a really big bass lover, is that they go down to only about 30-35 Hz -- they still don't quite plumb the depths.
3. You can pay less and get the Micro Utopias with only one cone speaker and the great tweeter (rather than the two speakers on the Mini). Even though the Micro Utopias are smaller than the Minis, the one speaker has a bigger box and produces a more pronounced bass sound. The bass isn't as realistic, however; it has an artificial boominess compared to the above options, and the midrange isn't as good as in the Minis.
4. You can get one of the top end versions of the Electra, the model just below the Utopias. A lot of the Utopia technology has now come down into the electra, including the W sandwich speaker cones and the time alignment placement of the speakers. You can get full bass and really great sound from the Electras, but not quite the amazing clarity of the Utopias, and not that ultimate tweeter technology.
5. Here's my own choice -- you can get a REL subwoofer -- I chose the Storm III. Heck, for the cost of a Utopia sub you can get two RELs, one for each channel. I think the RELs are the most truly musical subs out there. They have very sophisticated adjustments that let you blend them in with your main speakers so perfectly that you absolutely can't tell there's a sub in the room. The Storm is a "sub-bass" system that goes down to 15 Hz. The result is that for less than the Utopia sub, you can make your Minis sound not just like Mezzos but closer to full Utopias. The summer before last, JM Labs brought a big group of their US dealers over to France for wining and dining and touring the factory and listening to the whole line of speakers. The word spread through the whole group that this combination of Mini Utopias and REL subwoofers is a beautiful match.
Hope this helps. Bob O.