If the sub outs are not buffered and high pass filtered, and are merely connected in parallel with the main L/R outs, then when you connect the sub outs to a y adapter you will also mix the main L/R channels and make the whole system mono.
Stereo sub out to mono, is it safe?
My new integrated amp has L/R sub output and my sub only has a mono input. Is it safe to use a Y adapter to sum the L/R output to the mono input or will this cause a short? Thanks for your insight.