Many soundcards allow stacking of units however there is the physical limitation of your hard disk I/O which may not allow your computer to function with too many channels (more than 8 channels). MOTU has something listed on their site about this potential problem (check the tech specs or tech support pages there). Unless you have a 16+ buss mixer connected to the computer cards inputs / outputs why would you need this? If its because you need more giga outputs without doing submixing in the computer maybe you should consider running giga on two separate giga only computers that are networked with say an eight channel sound card in each computer. You would have 16 giga outs to your mixer without the performance limitations of the hard disk I/O that MOTU warns about; just an idea to consider.
I know I\'m mentioning it all the time, but thats because I like it, so here goes:
creamware luna 2 ($400) + z-link expansion card ($180) + 2x converter boxes á 8 i/os (2x $500) => 16 analog i/os (side effect, 16 digital i/os via adat interface on the z-link). Certainly not cheap, but then you also have 3 floating point dsps on the luna, per dsp you have each several times the audio processing power than your cpu can deliver if it were not doing something else most of the time additionally to audio processing. Best way to find out if you like it is to find a tolerant music shop there and rent the stuff for a day.
I run a giga P3 1 gig puter with a 2408 and Logic audio..24 outputs plus bussing..
I also have a P3 700 running a 2408 with gigastudio 96 and separate my drum sounds and end up close to 24 outs and don\'t have glitches.. I used to bump my gigapiano over to logic cause it sometimes gets a little busy and uses up alot a memory..
I use the adat I/O and have had no problems with latency or dependablilty..
I also have unplugged the giga 2408 for a session that need more single tracks in logic ..I shut em down and rebooted with the MOTU firewire thingy in the one card and boom 24 more I/O..
Perhaps the most reliable 16-channels GSIF interface I was lucky to choose among several others is Frontier Design Group DAKOTA card. The only trick is that DAKOTA itself does not produce any sound - you need ADAT converters on ends of two Lightpipe cables, i.e. two ADAT machines, suitable mikser with two ADAT optical sockets, anything ADAT. That\'s what I\'ve got in my studio and it works without a single hiccup.