Well, my subs (JL Audio) do not have a speaker (high level) connections, only RCA or XLR inputs, and I am going direct from my Lumin X1 to my mono blocks (no preamp). I did not want to use a Y adapter.
So, I purchased a Jenson ISO-Max unit that converts speaker outs (high impedance) to XLR (low impedance). Seems to work very well.
ozzy