When I first got my V2 (and I was using KM184's) I was running it into an unmodded SBM-1. I went RCA > RCA and set the V2 to about 20dB gain and around 7-8 on the SBM-1. Got great results.
Since the line inputs on the Fostex appear to be 1/4" TS, they are unbalanced. Have a nice set of RCA > 1/4" cables made. There is no point in using an balanced to unbalanced cable (maybe with a 10dB in-line attenuator). The attenuator could potentially reduce signal quality and if you have to unbalance the signal anyway, just go unbalanced all the way. Get a 1ft long unbalanced cable (keep it short) and you will be set. This is IMO of course, the best way to run this rig. You will be able to get a bit more gain from the V2 and not have to worry about overloading the line inputs on the Fostex.
Good luck!