I bought my SL3s in 1995 and they were my audio only/listening room speakers for 16 years (into home theater as mains after 2011). They are old. If you like the sound, a good suggestion is finding a newer model, used.
I've fiddled with lots of amps and bi-wiring and bi-amping the SL3s over those years. I've run them plenty loud with only 60 watts of solid state. Seems strange the woofers are distorting from the Rotel. Any idea what decibel level distortion starts at and the general frequency area? Low bass, mid bass?
And, I am sure the Rotel is NOT overpowering your speakers. it may have a low damping factor and woofer control; I don't know.
I'm now running single-wired mono-block Wyred 4 Sound SX500s on the SL3s with 500w or so into 4ohms and my woofers really 'woke up' when I moved from a mid-level AVR to separates for the five channels. W4S claims damping factor of 2000; I don't know if that mattered but the performance is remarkably better.
A Y splitter is fine for preamplier-out left and right channels. If using different amps be sure the dB gain level's are similar.