It's not clear if you are, but as a warning do not, upon pain of death, use the old 5-8 channel mode, except solely play back old mods written for it.
If you are going to use more than 4 channels, use Mix mode. The old 5-8 channel mode has absolutely no advantages of any kind whatsoever (at least in 8 channel mode) and a plethora of annoying limitations.
In contrast, everything you can do in 4 channel mode continues to work just fine in mix mode, including synthsounds, MIDI and you also get support for 16-bit samples (with some volume limitations), stereo samples (ie stereo sample playback from a single channel), channel panning and so on.
I've managed 6 channel mix mode with MIDI on a vanilla 2MB chip only A1200. However, I can't stress enough the improvement you'll get just from few MB of fast ram added to the trapdoor. In mix mode especially, samples in fast ram speed up the mixing allowing more channels / higher mix rates.
As for the PCMCIA ram, I'd actually advise removing it. Accessing it is more than likely slower than accessing the chip ram and if code and sample data are loaded into it, it's going to cripple playback.