http://www.soundonsound.com/sos/apr98/articles/unitor8.htmlhttp://www.soundonsound.com/sos/jan00/articles/emagicamt8.htmThe Unitor 8 was originally released with an RS-422 Mac serial port and an RS-232 Windows serial port (mk.i) but was re-released in a mk.ii version with an additional USB port. The AMT-8 was released only as one version with both serial ports and a USB port. The difference between the two is that the Unitor 8 has SMPTE and other advanced syncing features (both mk.i and mk.ii) and the AMT-8 does not. There's literally 0 difference as far as performance and speed between the two, they're the same box +/- syncing features.
You can connect them to your mac via the serial port, then daisy chain U8s/AMT8s in any order. It's all in the manual.
The best method for G4s however is plugging in the first unit into the USB port (doesn't matter which model goes first, it just needs a USB port at least), then connecting the 2nd unit with the 1st with the RS-422 Mac serial port. That'll get you a 16 channel midi interface. You can then daisy chain up to 7 or 8 more using a combination of the Windows/Mac serial ports to get you as many I/O as you'll ever need.
Only ONE box with a USB port is necessary. Usually you'll find the mk.ii Unitor or AMT-8 with a USB port, but if not, grab the mk.i for some additional daisy chaining in the future. You could theoretically start with either a mk.ii Unitor 8 or AMT-8 for USB connectivity, then have nothing but mk.1 Unitors daisy chained after that using the Mac/Windows serial ports. Only the first in the chain needs a USB port. It doesn't matter what's after that and in which order either.
The only thing to be wary of is that the wiring on the Mac/Windows serial cables are different and must be soldered differently. You can take a look at the pinouts in the manual
http://www.advancedaudiorentals.com/docs/Unitor%208%20en.pdfIf you've got a buttload of midi gear and you're running OS9 DAWs, there's no better way than this