Weakest Link in my system... Power Supply, DAC, or...

Hello OP

As others have posted, you listening room may be your constraint. My audiophile nephew told me in the past that he has gained the most impact by improving room acoustics. At first, I did not really dig that, until no matter what I do, the changes are just incremental. One day, I contacted ATS acoustics and spoke with their support. I told them my room and my gear. they suggest the panels and I just got everything they told me (see my profile) 

Once all installed and after a few days, I notice that I can bring up the volume and I can hear more into the music. I am a bit deft, but I am sensitive to tone, timbre and spatial differences. 

Since you have the PAP speakers, which i have heard, you are good to go. BUT!!! That speaker needs to integrate with the room; it is so ROOM dependent. The better the room acoustics, The better that sounds. IMHO, you will be best served with Room Acoustic treatments. 

Lastly you mentioned about Prima Luna upgrades (Caps and resistors). To me that is another topic all together. I am very familiar with this as my 845 Audio Note clone power amp was built with all premium parts such as Mundorf, Audio note and Dale resistors and Japan Irons. It was assembled that way. When we did a shootout between an Audio Research and VTL amp, my clone easily equaled the VTL and surpassed the AR.

Hope you find which path you want to take

Again, this was in IMHO only. 

Obviously the room, although it needs slightly unique solutions for open baffle speakers. I ran various models of open baffle Alon's for years, and I previously owned PL I can't recall if it was you or someone else, in any case there is recent thread on mods for your PL. Open baffles like to be well away from room boundaries, but then you may lose bass moving them out further into room. You could also try EL34 tubes with PL, I always preferred EL34 to KT family in push pulls, EL34 has magic mids the others can't match.

So, room becomes somewhat moot if audio specific treatments not allowed, just get the speakers well away from room boundaries. Clean power is where I'd go next with your system, don't cheap out here, dedicated lines and good grounds go a long way, assuming you can modify your electrical service. Power conditioner would also be at top of list for improvement, you'll get endless advice as to which one. Beyond that your dac is next weakest link, and r2r dac's not necessarily rolled on top, I have r2r and Sabre chip dac, implementation of any protocol or chip is key. Your system very nice foundation for excellent sound quality, don't need wholesale changes.

Getting larger listening space is most impactful. I do not spend any significant money to upgrade audio components.

My mathematical calculation:

Upgrade audio --- from $5,000 to $10,000 --> maybe 5 - 10% up, not 100%

Larger room/higher ceiling --- from 12 x 16 x 8 to 16 x 20 x 9 --> tremendous!

If you cannot change your room, perhaps you could have an easily moveable listening chair and use  near field listening when you alone are enjoying your music.. I have treated the room enough with pillows and bookcases so that most positions now sound good for my guests, but I could never achieve great imaging due to constraints on what I could do to the room. I sit about 5 feet from each speaker and the sound stage dimensions and imaging are beautiful from the sweet spot. 

If you can’t articulate what improvements you’re looking for, leave it all as is. 
If you’re itching to do something to your set up run two dedicated lines, one for digital and one for analog.