Dereck, Did you mean the Rotel is 125W? The SP17 is a preamp and doesn't power the speakers per se. However, my research indicates that the RB 1080 produces 200W @ 8 ohms. In
one review, the measurements indicated that the Burmester could be a tough speaker to drive. The AMT tweeter in the B25 is very revealing and many amplifiers can become hard sounding when driving difficult loads - the AMT will convey this in a heartbeat. There's also the possibility that what's bothering you is jitter from the source component.
There are many possibilities here. As mentioned above, we still need some info about your listening environment and what is is that you're unsatisfied with in your system (I know it can be hard to put into words sometimes).
I'm not disparaging the Rotel amp - it's a nice, solid component but I don't think it's in the same league as the SP17 and certainly not the B25s. More refined downstream components will reveal flaws in upstream components in most systems. Dick