Hi Lanchang,
Wow, what a system! The Duo Grosso's should be amazing. If your looking for new amps you should give the GRAAF GM-20 OTL a listen. You could even use them as monoblocks, they are not that expensive. Check out the webiste for specs, these are some of the best tube amps made at any price. The they have a very power full sounding 20 watts! Check out this combo with Viva's Linnea pre-amp. it's some of the best sound I've ever heard with Avantgardes. The Italians have it down when comes to tube amp design.
A great 300B amp is VAC's Renaissance Thirty/Thirty Triode amplifier. Not very expensive on the used market, one of the best 300B amps I've heard with Avantgarde. You can save yourself a lot dough with these amps, spending huge amounts on tube amplification doesn't always net the best results.
Have fun with your new Grosso's!
Vinyl9
