If a pre/pro is off limits, then look for a preamp that has two sets of main outs. Some will have 1 pair of XLR and another RCA.
I'm using a Primare P30 pre/pro and it is sonically superior to some 2-channel preamps in direct a/b comparisons in my home. One of which is highly rated as a class a preamp in Stereophile (not that that means anything).
Nevertheless, I'm using the RCA main outs for the sub and the XLR for the amp.
You could use Y-connectors but you always take the risk of degrading the signal.
I'm using a Primare P30 pre/pro and it is sonically superior to some 2-channel preamps in direct a/b comparisons in my home. One of which is highly rated as a class a preamp in Stereophile (not that that means anything).
Nevertheless, I'm using the RCA main outs for the sub and the XLR for the amp.
You could use Y-connectors but you always take the risk of degrading the signal.