Outlaw, most of us who go hardcore into Tascam recorders get matching Tascam mixers,.
so matching cabling and signal level is usually not an issue.
When you go from balanced to unbalanced, it depends on which way you're going with the signal, and intended cable lengths, etc, as to whether you'll need a "bump box" converter, line transformers or simple adapters. Tascam made bal-unbal line converter boxes, the LA-40 and LA-80, also Fostex made the 5030, all units classified as "bump boxes". You may need one.
It depends a lot on the mixer that you're using, and the outputs it provides,... f/i, a [blank] mixer with balanced TRS 1/4" output jacks. That's what you have, eh? Well, go to the [brand] bbs and SCOLD the mixer mfr for NOT making his I/O Tascam-compatible! Haha! Well, my friend, the all-Tascam or Tascam-dominant setup uses unbalanced RCA I/O, and if you stick with one brand solutions, it's never a problem.
The NIB 34B is a rare find, indeed, and is easily worth $400, or more, depending on the day. It's excellent value at $400-$500, and still good value at $500-$650. BTW, it does include original box, packing, orig manual and takeup reel. It depends on how badly you want it, doesn't it?... as to how much it's ultimately worth. I don't have an exact figure, but when brand new the 34B probably cost appx $1400, so $400+ for a NIB unit is not too shabby.
Yes, I do believe that this unit was purchased new and never used, as I believe this has happened in "real" life, at least once or twice that I know of,... haha. His loss, your [my] gain, haha. Do you want first-person testimonial,... on how I've purchase several recorders and put "ZERO" time on them? Dude, it happens,... especially with the "wanna-be" recording star, who purchases a bunch of nice equipment, and then nothing ever comes of it,... [like me?... another autobiographical statement?... you decide, ha.]