Currently running an SMSL AD18 for my whole setup, but I’m looking for an amp to power my vintage 990’s (600ohm) and anything else down the line. I’ve balanced modded them and my other 770’s. I’m open to tubes, but the amp has to be balanced capable. I’ve been considering the a90, Gustard H16 and possibly the a30 pro when it’s released soon? Any insight would be great.