Yes, I have a MOTU 828MKII that can take a single ADAT I/O, for a total of 8 more channels of I/O. giving you 2 built in pre's, 8 line inputs, plus the 8 channels via ADAT, that's 18 total inputs, about 750 bucks
MOTU 896 HD firewire has 8 mic pre's and will take one ADAT box for a total of 16 I/O about 1200 bucks (I think)
Both MOTU's also have a SPDIF I/O too, so 2 more I/O could be added with the right hardware.
I don't know of any firewire units that are "only" ADAT inputs, they all seem to have at least 8 line input channels of converters too.
If your laptop has a type II cardbus slot, you could get an RME digiface, that will allow up to 3 ADAT interfaces through the cardbus, for a total of 24 channels of I/O.
If you already have 2 of the Alesis boxes, then the RME digiface/cardbus solution for about a grand ( maybe a bit less) is probably your best bet, you'll have 16 channels I/O right off the bat, with the ability to add another 8 anytime you want.