The sampler acts like a tape machine, with each instance handling up to 2 channels (stereo). Presumably you could use two instances of the module, with most of the inputs and controls driven together, so it would record two copies of the material. Then for playback, you could have 4 tracks of the same material, which would give you the polyphony you seek. Or, to be accurate, multiphony.
When it was created, it was mainly expected to be used to "fly in" vocals to an existing mix, using the pitch and time change to improve the result. No reason why it can't be used otherwise, but this was the original thinking. (Or so I believe – it was a long time ago). It wasn't conceived as a keyboard-type sampler, but then again…..
SIMPSAMP or DLYSAMP are lighter modules, so you will be able to get more channels from it. There is little information on them (sorry). Look at 5310-5314 for some example presets using DLYSAMP -there is also a help page for it. SIMPSAMP appears to be pretty experimental, so you would have to work it out for yourself.
