sorry, VST(i) Output channels. You know, when routing a midi track through a VST instrument.
I never said all DX plugins caused problems, but some do.. poorly written or not, I would recommend not farting around with it to find out. I stopped using DX in Samp after losing a good half dozen sessions (wouldn't open until I disabled DX in the ini, and even then I lost a good deal of what I had done with the mix because of it)..
The reason not to do it on a VSTi output is that is where it happened the most, it gave some kind of mismatch error because I had used a DX plug on a VST channel, or something to that effect.