OK guys, I've had some time with both amps now and am here to report that you can't go wrong with either one. Both are just absolutely fantastic amps, however, they are very different sounding for sure. I'm not very good at putting in writing what I hear, but I'll do my best and hope it makes sense.
In my system the Stratos is more dynamic, has more punch, and better treble extension. This is an extremely detailed and fast amp, but I never felt it was etched or shrill sounding. Just very precise and accurate. Mid range and treble were much more forward and prominent than the Belles. The Stratos is just a very musical amp and I felt I could listen for hours without fatigue. PRAT was about as good as it gets. On the downside, I felt it sounded just a bit thin with some recordings and I prefer a little more bass volume. Many will say it's just accurate, and they might be correct, but I'm just speaking of personal preferences here.
The Belles is a different animal all together. I know you've probably read many times where a reviewer says a particular solid state amps sounds like tubes, but with the Belles it's true. Except the Belles has detail, bass control and extension a tube amp could only hope to emulate. The sound stage is wide and deep, much more so than the Odyssey. It's hard to explain, but it's just a more realistic sounding amplifier in my system. The Bass extension and control on this amp are as good as any I've ever heard. I don't really have a critical thing to say about this amp and this is the first time I think I've ever said that. It does run hot, but that's about it.
Best bang for the buck; Odyssey. Best overall sound, Belles 350 Reference at 3x the cost of the Odyssey, but to me worth it. BTW, a comparison between the Belles and the Mono Extremes would have been more fair and I'm sure more of a contest, but this is what I had and hopefully it will give you some insight.