I've got a ProTools LE rig, but I'm looking to pick up an inexpensive cassette 4-track to use for tracking to analog tape. I'm strongly considering the Tascam 424 series... What are the differences between the MKI, MKII, and MKIII models? Even though this is just a cassette 4-track, the best sound quality possible is paramount, so if one has better preamps than another, or if one has greater simplicity in it's design that leads to better sound quality, that would be my preference... Obviously the 2x tape speed is very important as well, but I think all the 424's have that, right? Also important as far as features goes would be I/O options... Do the input/output features differ on any of the versions? Any other extra features really take a back seat for me given that I'll be doing all mixing/editing, etc. in the Pro Tools realm... I just want decent preamps, and good analog sound quality. In that light, the older MKI units look like the most straight-forward... Any other recommendations?