Monitoring And Recording, Keeping tracks separately from monitor Options

[palmreader44]

Hope I, as a novice, can explain this: Here's my setup 1) an older Mac (G3 500mhz .5 gigs RAM) with OS 9.2 2) Motu 2408 interface with 324 PCI card 3) Digital Performer and 4) Older 4 channel mixer.
Here's the problem: I have a stereo audio mixdown of midi tracks that I want to monitor and simultaneously record Bass on a separate track so that I can apply plugins to the bass and not the mix. Then put the bass in after.
However, I have to use the mixer as a preamp to boost the bass, so that when I record the bass goes directly onto the audio tracks (or, I should say that the bass and the existing audio tracks get recorded together) instead of a separate track for the Bass only.
The Question: Is there a way, without any additional equiptment, that I can accomplish this? Hummm, I think I explained it.