Hi,...
Sorry for the late reply, but given what I know of your gear empire,...
I'd just use another Tascam Portastudio to bring 2 additional mics into the mix.
Use the 488's inputs 1 & 2 for the first two mics, as normal.
Plug the mic3 & mic4 into inputs 1 and 2 on the second Portastudio. Assign mic3/channel 1 to "buss left" and mic4/channel 2 to "buss right". Take the "Stereo L/R" outputs from the second Portastudio & plug them into the Line Inputs 3 & 4 on the 488, using an RCA-1/4" adapter cables or plugs.
On the 488, assign inputs 1, 2, 3 & 4 to Groups 1, 2, 3 & 4, respectively, while setting tracks 1-4 all on "Record-Enable/Record-Ready",... and off you go!
What this scenerio gets you is that you can record 4-simul with 4-mics on the 488, while using the internal preamps/eq on the 488 for 1 & 2, & using the input/EQ from the channel strip on the "external" Portastudio mixer for mics 3 & 4.
That seems to be an easy solution to me, given that you have several Portastudios to use in combination,... & doesn't require any additional purchases. Any similar external mixer of the non-Portastudio variety would also suffice.
If I had more time, I'd draw you a diagram, but hopefully this explanation is clear enough.
/DA
