Connecting a Consumer Stereo Pre-amp RCA to a Nakamichi MR-1

I just bought a Nakamichi MR-1 for my home stereo, not realizing that not having RCA plugs on the machine would be such a minefield. I want to run this to my pre-amp (a Harman/Kardon PT2500). I want to outline my understanding, and see where it is right or wrong.
(1) The MR-1 has both balanced +4dBm XLR inputs and outputs, and unbalanced -10DbV 1/4" inputs and outputs. From the MR-1 manual, the XLR is wired 1=ground, 2=cold, and 3= hot.
Question about item (1): what is the difference between dBm and dBV? Is a standard home stereo line -10dBV, but not dBm?
(2) The balanced line is a problem for a stereo pre-amp since it runs at +4 dB, while my stereo line is at -10dB. so I should use the 1/4" unbalanced inputs and outputs, which are at the typical levels for a stereo. While the +4db gain would be okay for the output, the input of a pre-amp's -10dB into the MR-1's +4db balanced input would result in very low recording input and hence a high S/N when recording.
Question about item (2): Would a +4dB input into my pre-amp cause any kind of overload distortion? Could I sufficiently boost the input into the MR-1's XLRs with a stereo pre-amp, where I had the pre-amp out go to the XLR input?
(3) Since the 1/4" plugs are unbalanced and at -10dBV, and -10dBV is standard line level, and since 1/4" plugs are always unbalanced and a consumer stereo pre-amp uses a standard -10dBV line level, then the easy and high fidelity thing to do is to adapt my MR-1's 1/4" unbalanced inputs and outputs to RCA males to go to and from the pre-amp. Right???
(4) I should keep my unbalanced cables as short as possible (is up to 12 feet okay?) to minimize interference, since unbalanced cables are subject to noise if long.

Okay, so have I got the right end of the stick here, or am I totally confused? Especially will the solution in (3) work well? If I am wrong about everything(!), what is the best (but simple) solution that includes my keeping the MR-1?