Yep, you need to be able to set up a high pass filter in a much lower range than the XLS provides for, as I said it's more about using a monitor/bass bin setup. I like the XLS amps for reputation, value (I bought during really good sales) and quiet fans, and in conjunction with Audyssey (or sometimes just Audyssey alone, don't bother with my bedroom or workshop setups but rather my 4 sub setup in my living room. I even use them for mains in a 2ch setup, and for subs otherwise.
Also, if you have a Umik you're probably using REW? REW and
miniDSP can work with REW.
@Verdinut why change the provided design to ported rather than the slot vent?