MIDI is an asynchronous (sent whenever, not synced to anything!) serial interface, runs at 31.25k bits per second. The MIDI spec allows 24ppq over this serial line as standard. That's 24 clocks per quarter note no matter what the internal ppq is. To quote the midi counsel directly:
"However, MIDI data being sent from a sequencer can include a number of different parts. On a given beat, there may be a large number of musical events which should occur virtually simultaneously. In this situation, many events will have to “wait their turn” to be transmitted over MIDI. Worse, different events will be delayed by different amounts of time (depending on how many events are queued up ahead of a given event). This can produce a kind of progressive rhythmic “smearing” that may be quite noticeable."
Anything higher is time-stamped when a serial packet gets recieved above & beyond this 24 ppq clock. But it takes a full millisecond to send 1 "note on" for instance (3 bytes at 31.25kbaud). Having higher PPQ just sets when that 1ms begins. (at 80 bpm and 96ppq, that's at best 7ms quantization...equivalent to 1/128 of a second (128Hz), definitely audible to the physical ear, but questionable to the subjective brain).
Since MIDI is serial, as is USB, etc, ...only 1 thing happens at a time. So when a PC plays something over your 8 port MIDI device, things that are intended to play simultaneously, simply don't.
I'll agree with the "Mmt8" being tighter *sometimes*(I think you meant Emagic Amt8)...when used with Logic the Amt8 pre-loads the MIDI data for a given clock (ppq tick) into the Amt8, then sends out ALL PORTS at the SAME TIME...so all your notes ARE tighter. This is a fact, and is why Emagic made the Amt8 series...having a studio with 24 MIDI ports driving an orchestra of modules gets fuNked very quickly. MOTU came out with something similar, but again your sequencer needs to support it. But for 1 port, this really makes no difference. Rememer though, high bpm means less time for each clock tick(ie- more resolution)...things don't get noticable until you slow things down. This is why nobody daisy chains their instruments...they have multiple ports instead (like 2 on the MPC).
As said before though...you quantize, and your quantizing to the 24ppq typically (unless you go over 32nd triplets - ie: 8 32nd notes per quarter, but to get triplets you need *3 (to get the accuracy needed), so 8*3=24ppq, get it?). But the multiple ports still stands even when quantized.
