... if I wanted to add another 4 channels I would just add another R-44 and a sync cable. Just my $.02
Using the 1/8" TRS cable will only sync the start and stop of two R-44's. It will NOT sync the clocks of the two decks and you will get time drift between them. However, you can successfully clock-sync two R-44's via S/PDIF through a USBPre2 and they will both sync to the clock of that pre. Or, you can go S/PDIF out from one R-44 into the digi-in of the other one. The second R-44 will "double" those two channels and you will only get 6 unique tracks total that way, but at least they will all be in sync.
Yep, you'd get a total of 6 different channels
either way (two R44s = 8 channels total, but with one pair duplicated) using the SPDIF input as the R44 clock.
Doesn't matter if that source is the USBPre2 or another R44. R44 always records the SPDIF input to one channel pair and can't simply sync clock using SPDIF while record separate analog inputs to those tracks.
edit- as acidjack notes below, the USBPre2 can lock to an external SPDIF input and pass that same clock to it's SPDIF output while substituting audio signal from it's own mic preamps. That does allow for 8 seperate clock sync'd channels on two R44s. You'd just need to time align the files from the two machines in post. Cool trick.Doing the same with the DR680 allows you to record up to 6 'other' analog input channels on the one machine. The main difference is that with the 680 you can choose to use the SPDIF input for clock input only and not record the SPDIF signal if it will just be a duplicate of what you are recording on the other machine. If you do record the SPDIF input you can record 8 channels total on one machine. Note: you can’t play all 8 channels back simultaneously from the 680, but that’s probably not a deal killer for anyone here.
I’ve personally talked with two people who have run R44s in a master/slave arrangement with the sync cable to get 8 channels total, who told me their clocks sync’d and they just needed to time align the files as the start/stop times were off by some milliseconds. But I also know some people here reported that didn’t work for them- instead start/stop worked with some milliseconds delay but clocks didn’t sync, even though the manual and at least one official video claims they will. Maybe some units will and some won’t.