I forgot to include that I currently have a 3-head Technics cassette deck from the early 90s. I am assuming that the Nak would have better playback ability than the Technics. I don't plan on doing much recording.
The Nak 480, while certainly not a bad machine, was one of their lowest common denominator decks. If it were a BMW, it would definitely be a 3 series, and I dont mean M3, more like 318i.
With cassette decks as cheap as they are I would consider a more substantial Nak (Timo makes a good suggestion), or just give the Technics a clean and stick with it.
Just my .02 as a former Nakamichi dealer during the heyday of the 480.
the nak 480 does have adjustable zenith and azimuth. in fact, it uses exactly the same transport as the top of the line 3 heads. the only difference is the head, which is a different head than the playback head in the 3 head models. the thing is, however, that the playback head in the 3 head models are significantly better than the two head ones.
you might be taking a chance, because while the 480 is a very decent machine, some of the technichs decks from the early 90's were surprisingly good for playback. if it is the auto reverse model, azimuth is easy, there should be a screw on each side of the head base where the head stops it's rotation.
either way you go, azimuth is the only adjustment you should worry about. you should adjust it for each tape you play, because the correct azimuth for playback will be the same as when it was recorded, not nessesarilly the perfect 90 degree, but at the same as the error if any that was present when it was recorded. adjusting the zenith would affect other adjustments. the nak 480 and 3 heads allow adjustment of azimuth without affecting the other adjustments. the auto reverse ones that have the azimuth adjustment at the end of the head rotation do this as well. most decks of the non- auto reverse type do not allow for azimuth adjustment without changing other parameters, except for the 480 and higher end 3 head naks. none will work as well for playback as one that is playing back at the correct azimuth, this is the most important adjustment. the 480 might be worth it just so you can do this with ease, and the same goes for a 3 head model, except you will get better sound with them.
I owned the Nak 480 a number of years, but the transport eventually gave out. That was with only modest use for about ten to tweleve years. My inclination is to think you can do as well or better with other used pieces from A'gon or maybe even a new mass market machine. Because I seldom use a deck any more, I replaced the expired Nak with a low-priced Sony with remote control, which I use to tape audio from selected TV programs.
I tried in vain to find info on the rs-b85. I'm afraid I can't be of much help on the quality of it, except to say that I have been impressed with the sound quality of some of these technics machines from this vintage. I haven't paid any attention at all to model numbers.
What will end up I think being the deciding facter I think is whether or not you are able to optimize the azimuth and do it easily. One think I should mention is that on at least one new technics deck it left the factory with it's azimuth so far off you could visually see it. So note that it may not only be horrendously off, but so could the deck that the tapes were recorded on. (this problem of the azimuth being off on decks from the factory is not unique to technics, and is actually more common than not on mass market decks).
When the azimuth is off, the highs roll of at an accelerated rate, the phase characteristics kill the depth, and the sound becomes dull and congested. If you are using dolby, the problem multiplies as the dolby playback is then trying to recreate the sound of something that is out of phase with what was recorded.
I would suggest trying to find the azimuth adjustment screw on your deck, it is the adjustment that controls the head's angle in relation to the tape travel, the head should be at a perfect 90 to the tape. you should not be able to see any error, but you might be able to identify which screw would be able to adjust it. Play a tape, and listen to it as you turn the screw. take care to note the position of the screwdriver, so you can get back to where you started if you have to. count how many turns or half turns you make in each direction as you hear the sound degrade, and then count the turns to the middle of that. I highlhy recommend having a pencil and paper handy as you do this to keep track. write down where you are at in relation to your starting point as well. This is the laymans way to do this. It works, you just have to be careful enough as you do it to keep track of where you are at.
If it seems to complicated on the technics machine, then the 480 would be a worthwhile way to go. It has toothed gears on the adjustments, so you can count the 'clicks' as you go. It is also clear which one is the azimuth adjustment.
The azinuth adjustment really is the most important one, and the deck that plays with the correct adjustment will always outperform any that is out. The nak dragon, the king of all naks, actually continually adjust it's azimuth automatically. the dr-1 has a nob for the user to adjust by ear. Some of the older nak's, the 680's self adjust the record head to match the play head. Note that for playback, it is not ideal to be at perfect adjustment to the tape travel, but to match perfectly the head to what is recorded on the tape.
I could not find the azimuth adjust on the Technics and neither could the technician at the hi-fi store. We both listened to both decks playing the same tapes. We both thought the Nak sounded better especially in the highs. He showed me how to adjust the azimuth on the 480. I ended up trading the Technics and paying $80 for the Nak. He also cleaned the heads for me.
Thanks for all your input.