Stingme...okay I think I've got it now. I just read the pertinent sections of the manual.
Check out the last section of page 23. It is a nice narrative summation about which I'm writing.
Your board is setup to feed eight discreet sources to an 8-track recorder.
As stated above, route channels 1~4 to groups 1~4 respectively, but ONLY TO THE GROUPS. I'll explain why in a moment...
Your aux sends can be confirgured pre or post fader via internal jumpers. There's a diagram on the page that talks about the channel aux controls to show you which jumper position does what, but you have to open the board up. IF YOU ARE NOT PLANNING ON NEEDING TO USE POST-FADE SENDS DURING TRACKING OR MIXDOWN, I SUGGEST CONFIGURING ALL SENDS TO BE PRE-FADE. I'm not shouting...just trying to add emphasis. If you DO need post-fade sends for your projects, let's discuss further.
Anyway, got yer auxes configured pre-fade? Okay. Channels 5~8 get routed to nowhere (all routing assignment switches unlatched or up). I'll explain why in a moment. As stated earlier send channel 5 to aux 1, channel 6 to aux 2, etc.
Now you have complete control over 8 discreet signals going from mixer channels 1~8 to 80-8 tracks 1~8 via the group 1~4 outs and the aux 1~4 outs.
This does tie up your aux buss, but it is, as far as I can tell in the manual, the way the manufacturer designed the board to work in your application. They even go to the point of emphasizing that the aux circuitry is the same as the group circuitry.
The idea now is to monitor what is going to tape via the 80-8's sync head. If you simply monitor the sync head during recording, select which tracks get monitored via the controls on the 80-8, then you can monitor those via the tape returns on the mixer for record monitoring, overdubs, etc. Just make sure all the RET buttons are latched (down...this will send your tape 1~8 returns directly to the main buss), and make sure that the SUB switches above the group faders are unlatched (up). This will ensure that the groups only go direct to the 80-8 (via the group out jacks) and not to the main buss. In this way your 8 mixer channels go solely to the 80-8 with full level control, and the only signals present at the main faders are the returns from the 80-8 which you can selectively monitor during tracking via the sync controls on the 80-8.
If you need separate headphone mixes you could accomplish this (albeit with a headphone amp) by panning your tape returns L and R as needed. This will give you two discreet mono mixes present at the L and R main outs with individual fader control for overall level. These would then go to two separate channels of a headphone amp.
Again, if you need post-fade effects during tracking, let's discuss further because there are options. Also, if you are printing effects on a track or two consider using your inserts for these as many outboard send effect processors do have mix capability allowing them to operate as a send effect on an insert patch, keeping your auxes free for tape sends.
If you decide to do it this way, you will need an 8-channel RCA to 1/4" TS snake for your tape returns, and a snake (or individual cables) with 4 XLR-F on one end (pins 2 and 3 jumpered together) and RCA's on the other, and another 4-channels of 1/4" TS to RCA for your mixer to 80-8 connections.
Hope this helps. Neat little mixer. Has some nice features for its small format.