[John_Toolbox]

Get more RAM. OSX likes RAM. I don't think it's your immediate problem, but it will be once you get this rig working. You'll want at least a Gigabyte of RAM.

The TDM Ribbon should have a little arrow on it that lines up with the corresponding connector on your card.

Try reseating the card in the PCI slot. If they aren't snapped all the way in, they won't work.
Do the little LEDs on the DSP farm light up when you boot the computer?(Boot it with the door open to verify this) I think the red LED indicates power, and the green one indicates connection to the TDM bus.(Or vice versa).

Somewhere on answerbase is listing of all correct slot numbers for various G4 models. You need to find this. Slot/card order is also very important.

Yes, mix cards will do up to 16 I/O's. A 1622 cable should have a DB60 on both ends, so you won't need a Y cable, just plug it right into the mix core. DSP farms are 8 channels, and don't entirely support some of the later interfaces like the ADAT bridge 24. You should be good to go on the hardware side with a QE farm, assuming it works okay. If everything is set up correctly on the hardware side, you might be running into a limitation of the later OS and Pro Tools version. If I remember, d24 support was dropped at Pro Tools 6.1, which might also have included the "classic" DSP farms.

I run a similar vintage rig, but don't use OSX for Pro Tools. OS9 with 5.1.3 is very stable, and most of my old plugins won't work in OSX. If you have an OS9.2 install disk and 5 bucks to buy a copy of 5.1.3 from the digistore, that's a good way to make sure it's not a limitation of the later OS and pro tools version.