If you want an external burner, definitely go with FireWire - especially since your iMacs have FireWire ports. You don't want to settle for USB 1.1 (12 Mbps max), when you have the much faster FireWire bus to use (400 Mbps max). A few years ago, I bought a pair of Sony's external (FireWire) CD-RW drives (CRX-160e), for use with my G3s and iMacs. They work well with Toast Titanium 5 (compatible with OS 9.x and up to 10.1.x), and even with the slow (by today's standards) 12-8-32 speeds, they're more than fast enough for the computers' processing speeds. While the mainstream manufacturers have phased out production of external CD-RW drives in favor of external DVD±RW drives, some retailers catering to owners of older computers (like "
Other World Computing") still package external CD-RW drives. You can always get an external 5.25" FireWire case and install an ATAPI burner of your choice in it.