Considering buying a CD transport

Charles1dad is right. If you want the very best sound quality, then the PS Audio PWT is it. It sounds wonderful even topping a couple of highly touted CEC players. 

I am currently using a Cambridge CXC cd transport with an Auralic Vega DAC and for $500,  the CXC/Vega sounds much better than I expected.  I replaced an old Krell KV 300cd that could no longer be repaired.  I was going to buy an AYRE CD player but could not justify the cost.  Besides, who knows how long it will be supported by the manufacturer.

A transport could help. I don't think it will reduce the treble of CDs per se - you shouldn't be losing that information anyway - but it can make the highs sound smoother while solidifying the foundation of the music (mid-bass down) which will balance the sound. Usually high jitter/bad transports sound very thin and weak which makes any recording brightness harder to take. Think of it more in terms of overall balance rather than one particular thing. 

Your poor experience with Blu-Ray transports does not surprise me. The clock circuits in video players is a lot messier compared to a dedicated Redbook player/transport that only needs a fixed clock for 44.1k. 

I don't have a ton of experience with transports but the best I have used was a now-discontinued April Music Stello top-loading CD player. With a Monarchy NM24 DAC, it was miles better than a mid-priced audiophile CD player (maybe Atoll) that my friend had. But my Onkyo DX-7555 CD player, which has a "high precision clock," was a close second and made a very musical transport that I was happy with. Unfortunately I tossed it because it was too big to fit in my cabinet, and replaced it with the cheaper C-7030 (~$150) which isn't nearly as good. I'd be willing to bet their C-7070 (~$700) is a pretty good transport for the money, but in that price range the Cambridge CXC is probably a better bet - it's on my list to try. 

Another thing to try is a PLL/signal conditioner like the Monarchy Audio DIP. Get the Classic one, without oversampling. It greatly reduces the gap between a mediocre and good transport and can add a lot of body to the sound. And yes, SPDIF cables do make a difference, as much as I hate to admit.

BTW, I am leery of spending a lot of money on a transport because at their heart is a mechanical system (the actual transport) which is prone to wear and breakdown, and with those parts becoming an endangered species repairs may be difficult and not cost effective. It's good to hear someone's PS Audio PWT is holding up well though.

If all you want to do is play CDs, this, from Sparkler Audio comes under your budget. I listened to it through headphones at the Newport show and it sounded rather nice.

The designer used to work with 47 Labs and you can see it in his model.
It comes with the 16 bit NOS DAC but you might be able to get just the spinner if that is all you need.

All the best,
Nonoise