More watts or better power ?

I see those speakers have a rear port. not knowing where your speakers are relative to walls/corners, they may be making more bass, but smearing things a speck.

While trying a sub, you might temporarily block the ports, just to learn something, it takes patience and time with familiar music.

the speakers will not be trying to make low bass after the crossover for the sub, so they will sound different anyway, so I would only mess with the ports AFTER I found a sub that I might keep.

My office, my old velodyne servo 1200 sub fell apart. I tried a single inexpensive sub, got lucky: not to add bass as much as to keep things from feeling a bit thin. Volume just enough, not aware of it unless I turn it off. That’s all you need to make a small system sound beyond small.

If you ever go for another preamp/integrated, I advise having pre-out main in. then you can send the primary need for power to the sub’s amp. both the amp and the speakers get a break.

You might try the monitor audio platinum 100 Gen 2
,I believe they are a better than the 
sonas Faber.

my experience with wattage is speaker amp matching.  While waiting for new speakers, tried my esoteric class a amp with paradigm speakers.they have excellent bass response using small bass drivers.  With the esoteric the current must have shunted to the midrange and tweeters and was awful.  With my new Fyne which have larger
cone drivers the sq is beyond description.  Same sensitivity and resistance but clearly different electrical behaviors.  

It sounds like you have the itch to upgrade not because you need to but you kind of want to. With that, it is more pressure testing each component and finding the weakest link in the chain.  You have a great system that is better than many so you can stand pat.  

And incidentally, what is the old saying about opinions?

To me, lack of a conditioner is first.  I legit think that will help reduce your noise floor and expand your soundstage.  Doesn't need to be crazy expensive to get the big benefit.   A Panamax or Furman will get you there while some of the higher end units will deliver incremental benefit.  I would spend less than $2K if I were you.  And incidentally, just because your amp won't benefit from a conditioner, doesn't mean your other components won't.  DACs and phono stages may not be high current, but the circuits are delicate and small variations can impact sound.  

Second, your DAC is very good for the money but, improvement can be had.  I think stepping up to a better DAC will give you a leap forward in terms of resolution and image.  I have a few customers who have that DAC and side-by-side comparisons with others have delivered surprising results.  

Third, cables are worth considering.  They can be borrowed for a test. ICs, power cables and speaker cables can make a difference.  Which has the biggest impact will vary from system to system.  In my main system, I upgraded from a modest pair of Kimber Kable speaker cables to Audioquest Robin Hood and it was like I got a new component.  It was huge.  In my other system, the same exchange made basically no difference.  The swap from Kimber Tonik to Audioquest Water was big.  Switch from Water to Fire was minimal.  You get my point. 

I have heard some extraordinary changes because of cables.  Both good and bad.  I get a lot of cable trades and some very expensive cables have had shockingly bad impacts on my system and some modest priced cables have been surprisingly good.  Borrow some and see if you like it.  Keep an open mind in both directions.  Expensive does not mean better.  

Your preamp, amp and your speakers are all very good.  I can recommend better but I am not sure you will get a big gain without spending, and I don't mean the $3-4K it would take to trade up to a PS Audio BHK 250.  Simply adding power can help with many speakers, but I am thinking that is not the case with those speakers.  I would focus on quality and PS Audio, Pass and Sonus Faber are very high quality. 

Incidentally, no, I don't think your system is mid-fi.   If you want to spend $10K+ for any of those components, yes, you will see some gains.  There may be some diamonds to be found a lower prices but not obvious ones that are better to me.  

Hope this helps and good luck

If I read your OP correctly your sole reason for asking is that the rated amp power is at the low end of the recommended range for your speakers.  Sorry…forget that and just enjoy the music.  You have an excellent system, well chosen to provide a quality listening experience in your small bedroom.  And yes, if you have to tinker, get some high quality jacketed CL rated speaker wire.  Transparent HP122 or similar.  You’ll have to crimp and solder terminals after you pull it through the basement though.