i used to keep the gain down for the reason that the internal mike would give 'orrible feedback over about 1/3 gain on the recorder when recording acoustics, having said that when playing in electrics [direct] the mix wasn't too bad. Indeed any parts that were out could be mixed by using the volume sliders for each track on playback.
I WAS going to finalise my masters by adjusting the sliders as above,playing the tape back through the amp and miking the amp up..but i lost funds/interest for doing this.
The worst thing was i'd forget what part i was supposed to be playing back over the main track..my brain is like a swiss thing full of holes.
i've never used my zoom with it,although knowing the recorder i'd leave the zoom patches at the standard volume and the recorder at 1/3. The worst thing with this recorder is that if you di a guitar and listen to it in headphones it severely limits your volume.
I'd suggest setting you rig the way you want, running a mic in a suitable position relative to the amp into the recorder.Set the gain at a fixed point and record your tracks using headphones [i stupidly forget these sometimes] making any adjustment to the rig rather than the recorder.
If i could overcome the feedback(of my cheap gear) i found this gave me a decent way of recording.. although other people may do it differently.
PS.. Pickup okay now then?
Accuracy,you say? hmm interesting concept..