Hmm...
Geez this IS a challenge because you are wanting to do, really, 3 different things at once...monitor inputs, monitor tape tracks, and record.
Another idea to consider: patch a individual track out to an input, like a PGM BUSS IN. That will allow you to monitor a tape track in the cue mix while also monitoring inputs and recording. Your limitation would be (as you've identified) the number PGM groups and tracks. If you are set on monitoring ez drummer in stereo, yes that takes up 2 PGM groups. That only leaves two groups, one for one tape track playback and one for recording on 1 tape track only. BUT, if you are only wanting to monitor ez drummer, you could assign it to 2 PGM groups the same as (for instance) 2 tape tracks you want to monitor (so if you want to listen to tracks 3 & 4, assign ez drummer to PGM 3 & 4, connect TAPE OUT 3 & 4 to PGM BUSS IN 3 & 4...you now are monitoring 2 tape tracks and ez drummer in stereo and you haven't touched PGM BUSS 1 or 2. Hope that makes sense. The volume level on the tape tracks will be fixed at the PGM BUSS IN jacks, so you would have to manipulate the level of the ez drummer inputs to get the right mix, and then of course use the monitor mix master and headphone level to get the right mix and level. But I think this would work.
I tried the Insert switch idea, but I didn't have any luck with it. Maybe I'm not entirely understanding what you're suggesting with it, but did try several things.
Regarding the above, I'm afraid I'm not 100% clear on what you're suggesting. I think I have kind of a grip on it, but then I lose you at some point.
I'm not set on monitoring EZDrummer in stereo at all. I don't care about that. (If I said that earlier, I shouldn't have.) Mono is fine, as it would only be a time-keeping device at this point. (I'll worry about the stereo image during mixdown.)
I did find two different workarounds tonight that will get the job done. It's not exactly as I'd imagined, but they both work. They both involve setting tracks to RMX after they're recorded.
Method A: Monitoring on an EFF mix
1. Push "EFF 1" switch in PHONES select switches.
2. Plug signal from computer (EZdrummer) into CH 5 and 6 Line B inputs.
3. Switch CH 1 (with recorded guitar already) to RMX mode.
4. Turn up EFF 1 knob on CHs 1, 5, and 6.
5. Plug instrument into CH 2 for recording. Switch to Mic/Line, assign to Buss 2, pan hard right, turn up EFF 1 knob (to hear the instrument), and set TRIM level. Push record button 2 switch.
6. Play and adjust mix using CH EFF 1 knobs. Everything will be in mono.
7. Start recording on TRK 2.
Method B: Monitoring PGM mix
1. Push "Monitor" switch in PHONES select switches.
2. Press "PGM/CUE button so that it's lit (in PGM mode).
3. Plug mono signal from computer (EZdrummer) into PGM BUSS 4.
3. Switch CH 1 (with recorded guitar already) to RMX mode, press assign 1 switch, and pan hard L.
5. Plug instrument into CH 2 for recording. Switch to Mic/Line, press assign 2 switch, pan hard right, and set TRIM level. Push record button 2 switch.
6. Play and adjust stereo mix with monitor pan and level knobs.
7. Start recording on TRK 2.
Both allow me to hear the computer's signal and tape signals while recording a new track. I'm not monitoring the cue mix in either scenario (as I thought I should/could after reading the manual), but the goal is being accomplished nonetheless.