Originally I used an ADC sound shaper SS315. It had 10 bands per channel, a calibrated microphone, a spectrum analyzer with a fluorescent display and was fairly expensive when I bought it around 1982 (about $300.) The power transformer failed about two years ago and I had to substitute another one which was at hand. I had a spare BSR EQ 110-X. It was made by the same parent company, had the same center frequencies but it didn't perform the same way. Duplicating the settings and a plug out/plug in did not give the same results. It probably took the better part of a year to get back to where I thought I had been. (I have two more of these tied up with another project.) Right now in my experimentation with the enhanced Bose 901s, I'm using the 10 band equalizer built into the Marantz SR 930 receiver.

I don't think it matters so much which model you use, it's how you use it. However, I would not use one that will not allow infinitely contiunous adjustment for each band, in other words, one that would restrict you to a 2db or 1db increment per adjustment. The exception might be a digital unit but 1 db would be the absolute outside limit. 2db is just too much of a range. One thing that amazed me is how I could tell even small changes in the settings once I head the same musical passage over and over again.

Good luck, this is a long frustrating job but in the end, you probably won't regret it. One more tip, write down your settings so that you can refer back to them. Date each profile. you might even want to take notes on what you heard and what effect your adjustments have. After a while, you can kind of predict approximately what you need to do to fix a particular problem. Sometimes your guess even turns out to be right.