Wilson Alexia 2 lacking some bass

I’m wondering if the amps may not be the ideal match or if further adjustments to the speaker placement could help resolve this.

You could keep changing amps and placement until blue in the face or.....the simpler solution is to get a pair of subs....

Placement is key, but the best bass response might not be the ideal placement for the mids and highs. A sub, or 2 under 50Hz with their own volume control might be the ticket for that last octave to really kick in.

The minor lack of low end response?  Compared to what?  Using a test frequency track can help pinpoint the exact frequencies involved.  That should be determined before any solution can be attempted.

+ 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