Tomryan,
That's exactly why I didn't like the solid state Simaudio Moon I-5 or Electrocompaniet ECI-3 with the 1SCs. I found that the 1SC's treble became excessively bright and the "ProAc midrange magic" was missing when driven by solid state gear. Using a tube DAC, tube preamp and a slightly dark solid state amp creates and entirely different and much more pleasing soundfield. That being said, I have heard ProAcs sound lean and bright in an all tube system as well. Tubes aren't necessarily the magic bullet, but may be the path with the most possibilities.
Pepler,
In the past, ProAc and ARC have been linked as a combination with great synergy. I heard an all ARC set up driving ProAc D80s a couple years ago at CES and thought it sounded very big and organic, but was a bit weak in the PRaT department. It could have also just been the show conditions or my personal taste in music reproduction.
I currently own the Response 1SC, Response 2.5 and Tablette 50 Signatures. Among them there's definitely a ProAc "family sound" present, but they also have slightly different characters much like siblings would in any family. The Tab 50 Sigs are quick and lively much like a person in their early twenties. The 1SC is the same person but at 35 years of age. A bit more settled and less inclined to take a misstep. After using both for almost three years with a subwoofer, I was shocked by the improvement when I purchased a pair of 2.5s locally earlier this year. The floorstanders actually image better than either monitor and the seamless, beautifully articulated bass is something that makes buying another subwoofer difficult to justify.