PS Audio Perfect Wave DAC upgrade to DSD?


PS Audio DAC users - I currently have a Perfect Wave DAC with Bridge II, and it seems to me that the next best upgrade to my system is to convert it to a DSD.  I am a neophyte audiophile on a budget, this purchase will be the only major upgrade affordable in the next 6-12 months, what can I expect in terms of SQ improvement?  

Rest of system is viewable on audiogon systems; the short version is Thiel CS 2.3s, BAT VK-55, decent power supply cables interconnects etc.  Weakest part of the sound to my ears is the high frequencies, sibilance and smear in particular.  Responses in prior posts have pointed out the speakers as a weak link, and that is another potential/next upgrade.  Room is fairly well treated but still being optimized.
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I bought the upgrade kit for my PWDII, and have been very, very happy to live with a DS Sr for a year now.  I liked the sound of the PWD a lot, but the DS betters it in every way.
My .02 would be to address the speakers before upgrading the DAC. Assuming your speakers really are the weak link (you said they are, so I’ll accept that), you will get much more bang for your buck by upgrading those or investing in room treatments.  However, if your heart is set on the DAC upgrade, the DSD is amazing and a worthy upgrade. You won’t be disappointed. Cheers.
The Stereophile measurements of the CS 2.3 show an irregular frequency response above the bass, including a lack of energy around 1 kHz and an sizeable rise in the higher frequencies. If you are having issues with sibilance -- it’s not you, it’s the speakers. Other reviewers pointed out "glare" and such.

Exaggerated HF can give killer dimensionality, "air", and that sort of thing, but it also can be really irritating.

I agree with those who suggest auditioning other speakers before changing the DAC. If you’re buying used, Google first to see if measurements are available, and consider models with smooth and reasonably flat, or slightly declining, HF response. They will sound less exciting but also less fatiguing and closer to the sound of a live concert.
I have a DSD, and would be hard pressed to find a better DAC out there for the money (and it keeps getting better with each successive firmware upgrade).  PS Audio does offer a no risk in home trial allowing you to weigh the virtues of a new DAC while you audition speakers.  In my case it was a significant upgrade in sound over the DAC in my Oppo UDP-205 player.  However, if the sibilance is intrinsic to the speakers, you’d be best served upgrading there first.