I've had good luck with the MOTU 828. It's especially nice if you have an analog modular setup. Expert Sleepers makes a program called "Silent Way" which lets you use the 828 to send control voltages to a modular or other synth with CV inputs. (I've heard rumor that you can use Silent Way with the H8000 as well…)
Word clock is important when you have more than two digital devices that have to talk to each other. If you have two digital boxes, one can be the clock master and the other can be the slave, but when you connect more than two, you'll need some kind of word clock distribution unit so that all devices are synchronized. If you only use the analog connections though, you won't need word clock…
Regards,
Doug
