Wilson Alexia 2 lacking some bass

+ 1 @onhwy61 and once determined then play around with speaker positioning.

Congrats on this excellent system!

As others mentioned, run a frequency test. These speakers should have solid bass. 

Wilson recommendation in a manual for my Sabrina is speaker to listening position should be 1.1 to 1.2 times the distance between speakers (measured between center of tweeters).  That works for me but no two rooms are alike. 
Experiment and see. Walk around the room while test tone is playing to see if you are dealing with a listening position located in a null point

Like westcoastaudiophile I see no preamplifier. If you are running straight from the DAC to the monos that could be your problem. Maybe look for a high end pre to match what is otherwise an incredibly good system, even if I don't like Wilson speakers.

Check out hte AM Acoustics room simulator.  You input your dimensions, and it helps you locate your speakers and listening area away from nodes/antinodes.

Two possibilities. One already mentioned, position in room. There are spots where base is poor or even almost doesn't exist. This is purely a factor of room dimensions and speaker position  in the room. Unfortunately the position for best mids and/or imaging are often not good positions for deep bass.

Second what do you base the lack of bass on? Is it measurement or listening to sources or even test records? How loud do you listen. Our ears roll off in the bass in relation to loudness. Our ears are flat around 100 dB(way too loud for ear health). Below that level the bass loss is because of ear roll off. And the roll off is extreme. I'm lazy and don't feel like looking it up but I recall 20 Hz being over around 15 dB at 80dB level(still loud for long term listening). Before the adoption of minimal controls we had things like bass controls and loudness controls to try to compensate for our ear response.