Add an external DAC. Make my Oppo UDP-205 a true top player

I am not sold on my Oppo UDP-205 audio reproduction.  .  It plays all formats, but audio needs improvement.   Looking for audiophiles that have felt the same a bought a DAC..  Which one did you buy.  What works really well?
andrei_nz Read your post w/great remembrance of the changes I experienced w/my Oppo 205 doing very similar changes you suggest. My base system (NPS 400 Counterpoint amp into Aerial 7b’s then, now 10mkII) was driven w/the 205 as source & pre-amp. My 1st upgrade was to use a Shunyata Delta NR PC for the 205 (beyond my Shunyata loom), which had some nice subtle changes.
By luck the Counterpoint had XLR inputs which the Oppo could drive, I added the base Bionics IC’s and it was glorious.
Experimenting internally w/the 205 I found the addition of the dampening material and a Bybee IQ over the power supply were nice upgrades. BUT Having been an old AQ Sorbo foot user for years, at the encouragement of my audio guru Duane @ Automated Lifestyles/Bettendorf I bought some StarSound Tech Brass feet and cups (the idea to drain energy out of chassis) WOW that made the 205 musical again. Am now looking into next step of DAC combo & like ideas various members have offered regarding outboard vs upgrade etc.
Oppomod transformer is said to give nice sonic improvement.
Cheap over the long run.
@dcaudio  -

With your budget, you could try a Naim nDAC combined with a Teddy Pardo TeddyXPS power supply.  Excellent sounding and very well built, both by companies with long excellent track records re service.  The pair would be under $2500.  The combination will see off any of the standalone DACs mentioned above. 

If you really wanted to go nuts and add streaming, you could do a used Naim NDS with the same Pardo TXPS; though an NDS would be $3-3.5K on its own (the Pardo TXPS is $1099 new) and requires a separate power supply. 
Agree that a separate DAC is a much better deal than an expensive mod of your Oppo. My Oppo is a 105 and I chose an LKS MH-DA004. Monster linear power supply, dual DAC chips, 3 femtoclocks, discrete jpeg analog stage and built like a brick. About $1500 with Amanero USB board. There’s a long thread here about it. I see now that it has a US distributer.
Did I say discrete jpeg?  It's been a long day:  Discrete JFET.