+1 to all of the above. Active Xovers need not be expensive and provide ultimate flexibility so as to achieve a seamless blend between mains/sub(s). Most provide some level of EQ, which will also help correct bass FR issues.I have run my F112 both with and without an active xover and the active route provides better integration.
When I ran it without the xover, I was running my then Vista's full range and running the sub at about 50Hz and below.
I'm now running it with the xover and crossing my CLS's over at 77Hz. The JL does 80Hz and down better then most.
You might also consider room treatments or bass traps, I have both.
Try to avoid redundant A/D conversions, if your other gear permits.