I use my LAM all the time for level control too, and you can still do that. I also never adjust the channel masters once I've set the channel balance correctly.
But nevertheless, if you want *unity gain* through the FX loop with the maximum signal level before clipping the FX unit, the way I described is the way to do it. If that's not what you want to do, forget the whole idea of unity gain - it really doesn't matter anyway unless you're planning to bypass the loop with the Select switch on the back. The FX loop footswitch doesn't do the same thing, it turns the loop on and off internally to the loop circuit. All that matters is that you get a good controllable sound with no clipping in the FX loop.
By the way, *do not* put a 12AT7 (or 12AY7, or 12AV7) in the V3 position, or V4 - you'll blow it. 12AX7, 12AU7 or 5751 only for these two.