Wilson Alexia 2 lacking some bass

Forgot to mention the obvious. Reflections act like tone controls. Excess refelctions will make a speaker sound bright. Tame the mid/treble reflections and often bass will emerge like a galleon at low tide.  Don't forget the ceiling, especially between listener and speaker.

@OP. Congratulations - very nice system. Wilson's bass is somewhat overdamped and some people don't like that particular characteristic - personally I do. That is the subjective impression of the bass as opposed to the measured frequency response the speaker is actually delivering. It would be worth trying a pair of Shunyata Typhon T30's which should bring more impact and dynamics in the bass. Also, despite what DCS say, I prefer the Rossini via a dedicated preamp, as opposed to driving power amps directly, which is what I assume you are doing.

I used to own Alexia 1's until moving up to Alexx V.  I tried adding subs to the Alexia's and it did not do much. Ultimately I think speaker position is key.

I also have the Alexia 2's.  I run it with Esoteric electronics.  The Alexia's bass is awesome is the word that comes to mind.  It's the sitting position that is the problem.  I found moving the sitting a couple of feet closer or further away from the speakers are areas of bass nulls.  Try it, move around your sitting position and see for yourself.

Suggest you try a good preamplifier in your system. My Bartok sounds great until I put the Conrad-Johnson ART88 pre back in the system. A much fuller more complete sound stage. Most, including now even Paul McGowan who fought the concept of a preamplifier, seem to find a more complete presentation with a pre in the system.