Wilson Alexia 2 lacking some bass

I owned Alexia2 for almost one year and just traded in for AlexiaV this week. In my experience Wilsons are never lack of bass response (not sure you meant 40hz deep bass or 80-100hz mid bass, and not sure you meant lack of bass volume or dynamics ?)  also how large is your listening area that the amp+speakers can fill with enough power ? 

I would try to move the speakers 1/4inch at a time, towards the front wall and see if it helps. Another thing I tried is to take away the grilles of bass drivers and it should give you 5% more dynamics or punch feel. 
 

I am not familiar with the preamp you are using , but another way to try is to adjust the gain on your preamp and see if that helps. 

I would add 2 Rel subwoofers like the S 510 or the S 812. I just added 2x S 500 with my Shindo Masseto and Montille amp and Fleetwood Deville SQ. Wish did it before, it is really a match made in heaven. Perfect bass , better coherence and live sounding.You won’t regret it, believe me, will take your system to another level.

I had a pair of Wilson Alexia’s and upgraded to the Alexia V.  Additionally, I have a pair of Rel S812’s next to each Alexia. I would check the distance from your back wall to the speaker and see if moving it around helps.  Are tour speakers tied in? That will also help with bass.  I added the Rel s812’s to ease the lower end on Alexia’s.  Having had Nagra equipment and demo’d before my final purchase I don’t think it could possible be the amps. Those are some of the finest products ever made.  Also, note that in Nagra uses Wilson speakers in many demos and at many of their shares so the components are a good match.  I think you need to demo a pre amp before doing anything else.  I’m sure your dealer would let you demo one to see if it fits in your system. 

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.