This is how I do it. Except that I have only bought one same manufacturers decks of same series. Not that sound is very different in recording heads, but easier to control levels etc. I think serializing is easy as fuck. I have never noticed any problem with sound if signal route is simply:
CD player out -> input tape 1, output to tape 2, output to tape 3, etc... Even 5-6 decks, and sound appears to be exactly same. Each deck has gain & balance buttons anyway, so it's easy to adjust this in way that each deck is pretty much once adjusted correct volume. After this you merely need to adjust CD player to 1st deck according to current dubbing project, and rest of decks are automatically correct.
I started now to listen samples of each tape I dub. Just quickly fast forward few minutes from beginning, check volume balance and sound quality from both sides that it's satisfactory. Now that tapes tend to cost even 7 euro each, I would assume making sure dubbing is suitable is mandatory. These days the blank tapes are so varied in quality, that even if recording levels appears to be good in process, better check out what actually was caught on tape. Sometimes even "all in red" noise dubbing on semi-faulty tape (for example pad below magnetic tape slightly out of place) can result that actually only couple lights blinking on one channel. Due tape being such a small "machine", now I tend to check that all is in order before I even start to dub. Like enough tension in "pad" to make proper magnetic head/tape connection etc.
