I also have 97dB fullrange speakers , Cain & Cain IM-Bens.
I've got Welborne DRD 300B monoblocks and the above mentioned 6 wpc Art Audio PX-25. The PX-25 is a far superior amp in term of drive, tonal richness/density, control, finesse, detail, soundstaging, depth, etc. Of course, it should be at 3x the price.
The PX-25's power supply is phenominal and provides massive amounts of current for complex passages. It really performs like something 5x the power. It seems like I have never gotten close to running out of steam. I'm not talking sheer volume, any amp can get the Bens to painful levels - in terms of grip and control of music. Although, my speakers have Fostex FE-E Sigma 168 6.5" fullrange single drivers.
Having said that....
Large scale classical/orchestra pieces really make unusual demands on any amp. You SAP speakers have that big 12" woofer and you have gotten used to the drive/reserve power of a 40 wpc parallel 845 amp. I'm not sure the PX is going equal that kind of power. It may outshine the Mastersound in all the other important sonic traits, but in sheer power - I dunno. (possible, though)
My guess would be the Art Audio 300B amps - Diavolvo(13 wpc), Jota(20 wpc), or high power Jota (30wpc and 40% more current drive) would be more comparable.
I talked to Joe fratus, the owner of Art Audio, about exactly this before getting the PX-25 and he told me that PX is his favorite amp for overall sound (he has the same speakers as I do) and the amp he uses at home even though he has far more expensive models. His advice was to go with the PX first and if I found that didn't have enough drive, then go to the Diavolo.
I would definetly call Joe and get his input. He's very, very, easy going and knowledgable. Loves to talk audio and isn't the type to try and force his most expensive product(or any) on you. His office # (401)825-8626. If he's not there, they are usually at the assembly shop (401)265-6765.Art Audio
Be sure to read the reviews section.
BTW, are your speakers really only 97dB?SAP J2001
The 12" woofers are 99dB, the mids 102dB, and tweets 105dB. I guess there's some efficiency loss for the crossover, but it seems to me those puppies should be around 99/100dB.
Hope some of this is of help.