will changing to solid-state make the bass in my wilson sophias better at low volume?

Hello,
The subs are a no brainer. I have two RELs and they really help out the bass at all volumes. You have to turn up the amp so much to get those divers moving on your front speakers. Not the case with subs. Next is the type of amp. Mark Levs have to be turned up so much before the bass engagement. On the other hand the Ayre AX5 integrated amp provide great bloom at all levels. Last is the preamp. I demoed the Rouge RP7 balanced preamp and it was so great at providing that bloom at very low volumes. This is with a SS amp. There is something awesome about a tube preamp with a SS amp. Like yin and yang. I am auditioning the Rouge RP5 preamp which has the phono preamp. Something very cool. You can turn the Phono preamp input into a line input in case you want to use your own phono stage and it has extra preouts for subs. Rouge is really good. If there is a Rouge dealer near you try out some of their gear. If you are in the Chicagoland area check out Holm Audio. https://holmaudio.com/

OP, look here first and gather some good information.

Servo bass units..

http://www.rythmikaudio.com/

With Wilsons.. Gotta be a good combo. Understand me, I know NOTHING about Wilson. I have two friend that are Watt Puppy fans. They have done everything to those things.. Wonderful speakers. They are SS bass and Valve mids and highs.. That took a bit of sorting..
All Mcintosh. MC275 and MC2300 and an original C22 all dolled up on one. 5 years ago..

BUT for you

A pair of 8" or 10" sealed servo. Talk to the rep it will be a Cubic Foot thing, and how you want to pressure the room.. alway add 2 more, Servo is REAL nice. Little boom BOOM in the Room ROOM.

Regards

Wilsons require high current amps to drive them properly. Also, triode is not the best mode for dynamics at any volume. Do you have an ultralinear mode on the amp that you can switch to?
In my Wilson travels (Sophia, WP7s, Sasha and now Alexia 2s), I have found that high current tube amps with 100 to 150 WPC are enough to push all of the above to satisfying dynamic levels. 250 WPC or more are even better. But at 75 WPC, it will depend on the manufacturer. Audio Research Ref 75 worked pretty well. Can’t say I know Cary well enough to render an opinion about the pairing that you’ve got.
I personally prefer Wilsons with all tube amplification. The bass is different than ss but sounds more live to me. But that’s just me.

I doubt it 

Taking a different tack, I had been in contact with Ayre due to bass complaints with my amp. Since they had no off-the-shelf mods for that unit, I looked to other factors. Long story short over several months, I found that for better bass in my system controlling the vibration for the equipment in the stereo rack helped immensely. I used IsoAcoustic Orea pods under amp, iso transformer, and DAC vs. blocks, cones and other options. Would have added a set under my Ayre pre but i have no vertical room for it. Second,  testing different DC power chords between Uptown LPS 1.2 and Ultra Rendu, and keeping it cheap (so far) to improve bass, I ended up with with Cable Matters, written about extensively in different forums. These seemed to give the power back to the bass region, though they were not perfect. Third, were better PC's. I use Cerious and each new chord beefs up the bass naturally. And fourth were improved plugs from the Topaz Iso Transformer to the wall, and for the charging unit for the EtherRegan. So, no equipment changes and i got improvements that probably needed to be made anyway that were somewhat close to an amp change. 
I should add that before any of this, I spent several days retesting speaker placement and due to the first and second changes above, retested again and might slight movements. It all matters.