there's a little box called "direct monitoring" in the cubase vst panel. unclicking this seems to have FINALLY broken through the sample rate issue and given me the sound i remember. that means i'm going to have to go back over this one more time. but it seems to be the answer i've been trying to figure out.
i'm not entirely clear on what this does. it appears to be related to whether i can hear files coming in from the mixer or not. if i was running an input driver all the time, i may have screwed up the output driver. i dunno, that's a guess.
but, i'm feeling good about this. now, though, is sleep...
if i go back to this feeling i was having that i was being eavesdropped on, it kind of adds up. it's probably obvious that i have unusually sensitive ears. the direct monitoring takes the input from the mixer and sends it to the output. just the bandwidth could have been bothering me.
there's been nothing attached to the input the whole time, of course - i've been mixing old four track parts. so, if that's what it was, it's, like, a virtual ground loop on the signal.