I have heard my integrated amplifier (Opera Audio Consonance a120 Hybrid Integrated Stereo) drive a pair of GR-10s. I thought it sounded great. If it were me, I'd dump the AVC2500u and get a high-end integrated amp. Preferrably one which has a tubed line stage (preamp section) and solid-state output (power amp section).
p.s. Disclaimer: I have my a120 for sale in the classifieds on this forum, but none the less, a hybrid integrated really is great and convenient for 2-channel. For example, the a120 has two sets of outputs, one I used for line inputs to my powered subwoofer.
Seriously, check out a hybrid integrated stereo amp.