WaveLab7 will record from front (mic) inouts, but not Line 3 & 4 inputs at back of interface

[Classicrock1]

I have WaveLab 7, and my system is a PC with Core i7-860, 16GB RAM, and PreSonus Firestudio Mobile interface connected to myPC via FireWire 800. The PC runs Windows 7 Home Premium 64-bit SP1.

Normally, things seem to work well (I upgraded to the full 16GB of RAM allowed by my version of Windows this past weekend), but I have one issue that I can't seem to resolve: I have some original music that I mixed down to 2-track stereo on DAT tapes. I wanted to transfer these music files to my PC via WaveLab, then burn them to a CD.

Whie my DAT machine is still in good condition and operates well, I realize that the format is obsolete, the tapes are delicate and don't store well long-term, and the machines are finicky and prone to failure.

The problem is this: for some reason, WaveLab accepts input signals from my Alesis Studio 32 board (from the Main Outs) through the 2 front mic/instrument inputs (combination XLR/1/4" jacks), but when I plug the cables from the board into two rear line inputs, no signal registers (no green bars when record is enabled). I have established that signal is indeed coming in on those two inputs because Universal Control (Presonus's mixer app for this interface) shows input signal on them, and I can record an audio track into Cubase or Studio One, but WaveLab ignores those inputs. I can work around this by plugging the cables from the board into the front jacks, but I would rather use the back ones. Does anybody know how I can enable those back inputs in WaveLab? Thanks.