Bose 901 VI flat?

     I had a pair of series II from new into the 90's when the Bose 500 watt "arc welder" Amp shorted for the second time and took out 1 amp channel and all 9 drivers on that side.  Sorry but back in the day the bass was way bigger than roomy's L100s, probably not as accurate/tight.

  I now use the remaining one as the rear surround in a 7.1 HT.  I use the Atmos level amp to simulate the EQ with the room correction...works pretty well spreading the ok sound on the back wall.  One of the pedestals support my stand alone reference headphone system.  Agreed they need a lot of omph!

I have sold HiFi since 1973. Whenever a Bose 901 owner asks me about electronics to drive them, the first thing I stress is that modern AV receivers generally cannot be used due to their lacking a tape monitor. You must have a tape loop or processor loop or “game over”!  A fallback is to put the EQ between preamp and amp, but very few AVRs allow for that either. So the OP needs to find some suitable amp, and it’s not going to be anything like his Sony. Even used, it’s likely to cost quite a bit more. A really vintage receiver would also need recapping. The cheapest modern solution is a Wiim Pro front end as preamp and a used beefy power amp with the EQ in between. 

Everyone stressing the importance of using the Bose dedicated EQ is right on. I bought a used pair years ago which came with the EQ. Since I already had a very good 10 band EQ I thought it would be better than the Bose. Like you say...They sounded "flat".

I also read that the speaker foam surrounds deteriorate with age and, upon removing the grills, found that was the case. Bought a kit and replaced the surrounds. Still no improvement. For the heck of it I hooked up the Bose EQ. Sound was much better but still "flat". The speakers just don't match up to a lot of others for much less that the cost of the 901's.

Bose sounding flat? I agree that’s the case. I’ve tried multiple high power vintage receivers and they are incredibly dull and lifeless. I thought that maybe the Eq was bad and was going to buy another one but after reading this the speakers must not be my cup of tea.

I own 1968 Series 1's. Even if the OP has Series 6's which don't I have experience with. Just get a minDSP from Amazon for $125 (100% money back) and dial in the curve for the Series 5 or 6. If the OP likes what he hears. Awesome !

I run Klipsch Cornwall IV's with a 500WPC GaN FET Amplifier and swap in the 901's on occasion for fun. They are great Speakers for what they do. No, you can't hear the fart of a Nat like I can with the CW4's. But I still enjoy what they. No foam rot either cause the Series 1's and 2's (which I also own) are cloth doped surrounds. If the OP's Series 6's are the V2 with the "rolly" surrounds. Foam rot shouldn't be a problem.