Re: Doing some research, looking for an under 30w tube amp
I might go PA, too. Use the Fishman pickup through the amp, and then a mic with a Shure sm57 on a boom. She can step back from the mic when she's not soloing, then into it for solos. A 57 will add some fatness--might be better than a condenser mic in this case.
Or you could hook her up with something like her own amp head and cab. Like a old used Peavey XR600C/D/E PA top box. Good eq, good power, flexible patching. Speaker? SP-2 or SP-5; or a floor monitor like the Yamaha SM15IV. You can go 12" in or 15" woofer, whichever sounds best.
Or you could try one of the small PV, Mackie or Behringer non-powered mixers into a POWERED PA cab--Peavey, JBL EON, EV, QSC, Mackie, Tapco, Carvin and Behringer, etc. They can usually be tilted back into a floor monitor. Add whatever processor you need--EQ, reverb, delay, compression--between the mixer and the power speaker.
Another option is use a bass or keyboard amp, like a PV KB-300 or a TNT150 or the all-purpose Nashville mentioned above. I think a guitar amp has too much top end emphasis to use with the Fishman and the violin.
Here's another sleeper--the 50 watt Acoustic Control AB50 has a 10" and a piezo tweeter. Designed for an acoustic bass, very portable and versatle little amp--but no effects. I have two of them for use with an Alesis Drum Machine, but have used them for PA, guitar, mandolin and electric bass. Available at Guitar Center. Inexpensive and highly recommended.
Have you tried the Fishman acoustic guitar amps like the Loudbox--they are voiced for their pickups. They should be able to cut through; but you could also mic it or use the DI. I wonder if Fishman has an AURA patch for the violin? Hmmm? THAT would be very cool and useful.
And take a look at the Radial Tonebone PZ Pre-amp--it's designed for piezo pickups.
There's lots of ways to get it done. Good luck!
Bill