DACT has a 10k, 0 to -12 dB in 0.5 dB steps, "fine tuning" attenuator that can tame different amps. Easy enough to add series resistance if required (50K for some tube preamps). Inline with the "stronger" amp after the Y. Another pair of IC's, a small project box (Goldpoint?) and a drill, a knob, 4 female RCAs, hook-up wire and a bit of soldering.
Don't try this with pots.
Don't try this with pots.