If a firewire drive doesn't mount or comes up as "eject or initialize". HIT EJECT!!
Try to run disk warrior to see if that can fix the problem.
The FW bus can only run as fast as the slowest device on it. Although Macs, PCs, and most drives should be talking S400 (400 Mbit/sec), many cameras and decks, both consumer and pro, only support S100 or S200 speeds. If you hang an S100 deck on your bus, you've just cut max throughput by a factor of four...
If playback is stalling, try disconnecting some, or all, of your Firewire drives. Although the Firewire spec allows up to 63 devices to be connected to your computer, after about five or six drives, there's so much "talking" on the Firewire bus that performance really starts to degrade. Where possible, limit the number of Firewire drives you are using. Worst case, buy bigger drivers and copy data from smaller drives to bigger drives so you total storage remains the same, but the number of devices decreases.
Good firewire rules: