Chris B,
For more input on the hiss noise: Using the ZR1600 via XLR with an Anthem AVM-20, VMPS RM/X, the hiss is audible from about 3 feet away. The original ZR 1600 amp fan was audible from at least 20 feet away. The swapped fan (Pabst?) is audible from about 4 feet away from the amp.
For reference, the Panasonic XR45 was not audible at all, and the Krell KSA-50S was a little less than the Carver.
Sounds like Audioengr is on track with making an already tremendous amplifier even better!