The Bose 901 series are notorious for being finicky about placement and, even then, the results are questionable.
Your belief about a vintage setup with "real" tape monitor facilities is wrong. that EQ can go anywhere in the signal path and is, I believe, alreeady in a "real" tape loop configuration with your current amp.
Final diagnosis: Keep the amp, replace the sepeakers. I'd suggest floorstanders.
And, keep in mind that to learn music, a kick *** stereo isn't mandatory. You would be surprised at how many musicians couldn't really care less about the audiophile quality of their sound reproduction equipment. They listen to the music, not the equipment.