Okay, first up, Jeff the Tascam Guy, hangs out here some. If you're lucky maybe he'll chime in, but you may have to start a new thread naming him or at least mentioning Tascam to make sure he checks it out. He knows way me about their products.
For example, about 5/6 & 7/8. I've only ever used those effect returns. I'd assume they're set to a nominal level and you just try not to overdrive them with your input level. But what tracks do they record to? I dunno. Mine's lived in the closet since I got my DAW. If you have the manual, read it and tell me. If you don't, go to Tascam.com. It may be available as a pdf, or you may find your answer.
So you're recording the whole ensemble live in one pass, no overdubs planned, right? Good for you. Much less labor intensive and suited to the limitations of a 4-tracker. It means having very limited flexibility for adjusting each instruments level after the fact, but if you test for levels as you go, you can make adjustments on the fly and sorta mix as you track.
That Ampeg bass head, does it have other output options? If so, try them. I tracked one recently where we finally gave up trying to get a usable signal from it and just mic'd the cabinet. If you don't need the sound of the bass in the room, you might consider just taking a direct box or instrument preamp into a track input. If you have access to neither, you could try plugging it into one of your mixer's inputs and record it with the drums. Line splitters are handy toys when you need the amp sound in the room, but want to record via DI.
Hey, just thought of something. I'm not sure about the mkII, but how are the input trims set for your mixer channels? I know mine had little sliders for each of 1-4. With the channel fader set in the nominal position (about 3/4 of the way to max) you set the input trim for only as much as is necessary to get a good strong signal to tape, judging by your meters and ears (by listening to playback). Too high and you'll get extra noise.
You never said what outputs you use on your mixer. I'm not familiar with any of radio shack's mixers, but I assume you're talking about L/R stereo outs? If so, are you able to adjust the master output level on the mixer? How is that set? Does changing the mixers output level have any effect on the signal you record on the Tascam? It certainly should. On the 414, is there a switch for "Effect/Monitor", and how is it set?
As for the 5/6 & 7/8 stereo or mono thing, I used my as mono returns for my delay and reverbs. But I believe, and again check your manual or the website, they are capable of receiving a stereo signal via TRS cable. If I'm right, you should be able to use a TRS Y-cable to take the L/R outputs of your mixer to either stereo input and have it record a stereo signal onto tracks 1 & 2. And I may be full of it.
Here's an alternate suggestion. Run everything in mono and give each element its own track: drums, bass, guitars, vocals. It means getting the micing right during the session, but allows the ability to mix each element separately after the fact.
-kent
