The bass boominess is an odd issue to have, esp with the XLS.. they aren't a boomy or bass-heavy speaker, by any means.
It's likely to either be a room issue, or you're simply use to your old speakers having a rasied top end or weak bass, so matching the volume means the lower mids & bass will be more present, since the XLS is a rather balanced speaker.
I know others have mentioned reducing the stuffing if its too full.
But aside from that and the suggestions that others have made, im not sure there's much else that can be done or tried without more info...
A simple frequency response graph of one speaker at a time in your room from the listening position may help give us some more useful info to help you with your problem