I am kind of new with the Bose 901. I have a set of refoamed series IV with stands and a Sansui 9090 hooked up. The sound last night was so awesome and better than pretty much anything I've heard (I have 7 sets of speakers). Clear highs, accurate mids, deep bass and all this at low volume. The 9090 is rebuilt.
They key to these speakers is to use the Bose EQs. Nothing else will give you the curve. I have a 10 band EQ and it does not even come close. You must set the Bose EQ at the beginning of every CD played and in corrillation to the volume level. More volume, less Bass and Treble, newer CD cut with loudness, run the EQ at minimum.
I also run a Bose 901 series I set with another series IV Bose EQ with great results. There are really some things that the 901s do very well, for one thing it is reproducing life-like mids.
From the unported series 1 or 2, the bass can be a bit less. I recapped both the EQs by replacing the 10 electorlytic capacitors and that brought the speakers to life.