Hello ming,
The H9 operated at instrument level, though it could take signals up to line level. Have you tried operating the H90 at instrument level instead? Taking a look at the JCM 2000 manual, I see there is a “LOOP LEVEL” knob that can be used to match an effects processor in the loop. If you prefer to run the H90 at line level, you may need to adjust this knob to match the right operating level. My advice would be to use one of H90’s INIT Programs which can be found on the User 2 playlist. It simply consists of to THRU utility algorithms. The idea is the level when the H90 is bypassed should match the level when the H90 is active. Adjust this loop level knob accordingly.
