UPDATE:
Actually, nope, this did NOT work. Massive PITA. Sending the Tascam back & just going to have to buy 2 x 2-channel preamps instead by the looks of it.
Sorry in advance for a small rant... I do not understand the thinking of Tascam in how they have designed this.
The Tascam "works" but for some reason best known to itself seems to have no channel separation at all when run as a standalone preamp.
Testing it now - I plug a mono synth into the channel 1 input, & it comes out lovely & clear on channel 1 output as expected = yay.
BUT it also comes out on channels 2, 3 & 4.... WTF.
Testing it with 1 mono input I'm swapping in turn between chs 1-4. Testing using 1 balanced output (mono) which I'm outputting in turn from chs 1-4.
I would assume, for example, inputting on ch1 with my output lead on ch 3 would result in silence - Nope. Same for all in/out combinations. Bizarre. It's like the device is mixing the signals internally automatically. Why on earth would they do this?
(I've been recording since 1995 & mixing & mastering has been my main job for over 18 years by the way, so I do have a small clue about this stuff).
I just wanted a simple 4 channel balanced in/out preamp unit I could plug something in to ch1 & have it come out of ch1 only... Same for ch2, 3 & 4. Simple.
Why Tascam have used this bizarre architecture is beyond me. Perhaps they see it as a "feature". God only knows.
I have no intention of using it as a computer interface, but loaded up the software to see if the internal routing was adjustable via software. Tried every option combination available in the software - nope.
Also tried plugging a silent jack into ch2 in case it was automatically putting a single jack-in to stereo (I suppose that could be a useful feature for some people) - no. Tried the same on the equivalent output with a silent jack inserted. Still no.
I'm sure it works great as a computer interface, but anyone looking to buy this as a simple standalone 4-in, 4-out all-balanced preamp don't bother.
Seems an utterly bizarre design. Unless my unit is faulty. Either way it's going back.
Oh well, back to the drawing board, & shopping for 2 x 2-channel pres instead.