Splitting line level out from preamp, versus using 2nd set of outputs

A splitter made the sound worse for me. When I needed this same feature (amps), I purchased the CODA 07x preamp which has 2 sets of XLRs. This sounded much better than a splitter.

In my case, 1 amp drove speakers and the other amp dove my RAAL SR1a earphones.

Today, I use a Schitt Kara F preamp to do the same thing.

i split single outputs into an amp and a subwoofer. im very pleased with it. 

The OP is trying to avoid buying another 4M cable from the sound of it.  The Y connector should 1M>2F with the male plugged into the amp driving the high frequencies, and the short cable into the low frequency amp, assuming passive biamplification is the objective.  A preamp with dual outputs effectively has a splitter built in.

I would like to avoid buying another $$$ interconnect, and I’d like to leave everything where it currently sits (equipment on left side amplifier(s) between speakers.

i would be adding a second amplifier and bi-amplifying one set of bi-wireable speakers

Neither amp has a line level out, and those are some great suggestions to keep the signal clean.

I'm 76, over the many years, I've used Y splitters for this and that, and it's never been discernable to me or my friends that help me listen for any problems/differences.

I just gave an old 4 way Video Switch to a friend, he used it backwards to select between two TTs, works great, no more switching cables manually.