I was just looking at the manual online for the C-4, and it wasn't clear to me if it allowed you to run two amps at the same time. I see that it has two sets of pre-outs, but the manual says to select a or b, not and/or. The M-4 that I picked up cheap was dropped off at my tech's shop yesterday, so I should know in a few days what the humming problem is that scared off the other eBay buyers. In the meantime, I'm trying to decide what Yamaha Pre-Amp to mate the M-4 with. I'm leaning towards the C-4, for the matching looks, but am open to finding a newer model as well. What's the consensus on the best bang for the buck Yamaha Pre? I'm in the under $150 shipped budget category.