coincidentally, if you do a google search for Tascam 488, one of the first hits that comes up is
http://www.homerecording.com/tas488.html
small world right?
Here's what I copied:
MIC/LINE INPUT (Ch.1, Ch.2) (XLR type connector x 2)
Input Impedance: 2.8k ohms
Nominal Input Level: -60 dBV (1mV) (MIC position)
-20 dBV (0.1 V) (LINE position)
Maximum Input Level: +5 dBV (1.8 V) at Trim Min.
MIC/LINE INPUT, Ch.1-2 (1/4" phone jack x 2)
Input Impedance: 5.8k ohms
Nominal Input Level: -50 dBV (3mV) (MIC position)
-10 dBV (0.3 V) (LINE position)
Maximum Input Level: +5 dBV (1.8 V) at Trim Min.
STEREO INPUT, Ch.9-12 (1/4" phone jack x 4)
Input Impedance: 10k ohms
Nominal Input Level: -10 dBV (0.3 V)
Maximum Input Level: + 5 dBV (1.8 V)
So this makes it sound like the inputs DO have a mic/line switch. Similiar to what I was talking about on my old Fostex. When I first started out with this post, I thought the Tascam was some sort of console, but I once I realized we were talking about a multi-track cassette, I was on the same page with you.
I use to plug in SM58s using an XLR -->TS connection to my old Fostex, but it did have a level switch, and even then I never felt like I could get all the gain out of it that I wanted.
Anyway, glad you found your answer.