At what point is an external D/A converter warranted or beneficial


Over the years and after multiple "upgrades" I've become disillusioned with digital audio reproduction. As my systems improved in quality/resolution, the digital audio quality has equally deteriorated to where most listening is now done in analog. This makes my CD collection of in excess of 1000 titles pretty much useless. My digital D/A conversion knowledge is pretty much limited to whatever is done by the internal D/A converter of the equipment. That being a Lexicon MC12B processor and Oppo BDP103. As my choices of ICs went from basics to high quality resolution improved with a marked decline in digital SQ. I'm at a point where any Redbook CD presents a harsh, edgy, shrilly, bright, name it what you want, upper frequency. Changing ICs back to basic cables attenuates this along with resolution of the music played. You might say I'm at a loss. Do I live with less resolution or the digital limitations. I do not have this issue playing analog media. Would an external D/A converter be beneficial or a waste of money? 
Systems are: B&W 803D2 and surrounds,  Lexicon MC12B, Oppo BDP 103, AQ Columbia ICs XLR & RCA,  AQ Digital ICs,  Tara Labs speaker cables,  Rogue Pharaoh, VPI Prime . Analog front end shares the L/R front speaker and input from the Oppo. 
Is there such a thing as an external D/A converter for a H/T setup as the Lexicon processor is the oldest piece in the chain with most likely the weakest D/A converter. But how would that connect to avoid the internal processing.
Any suggestions or recommendations?

128x128gillatgh
gillatgh
The Oppo is a pretty decent contraption.  My brother has the 105 and I noticed that it produced better sound in two channel than in 5.1.  There is some great Chi-Fi (eg Gustard X-26) running the latest ESS 9038 chip that could do you well in two channel.  You could use the Oppo as transport and the dedicated DAC for your two channell.  Also Okto will be putting out an 8 Channel that that has the best specs.  
https://www.oktoresearch.com/dac8pro.htm
I will be getting one.

Find yourself a nos dac Tube , some dac sound so digital which is a big turn off for long listen periods that not what you want , what you want is a analog sounding from your digital front end   I got a mhdt labs pagoda with balance and tube buffer sound very analog and natural   Hope that help 
Nobel100’s suggestion is the best/most comprehensive one given gillatgh’s current setup (I was only initially thinking 2Ch stereo, but you can test the system on all fronts with his suggestion).  You’ll also get the bass management and more up to date processing features.  I still have an Oppo UDP205 in my system for video processing and I recall some time back with one of the firmware upgrades that four digital filtering options were subsequently added for those using it as a CD transport (which I did for some time an was quite happy).  Not sure if this option was extended to the BDP103 (make sure you have the latest firmware version anyway).  Anxious to hear your results/conclusions. 
I don't have analog to compare to, but I had similar issues when starting to build my current digital system - harsh and bright - and had the same starting point with the Oppo 103 transport/DAC.  I did pretty much what has been suggested above - first I added an external DAC (used PS Audio Digilink III) which gave me more detail but didn't help with brightness.  Then replaced that with PS Audio Perfect Wave DAC and Bridge server, which quickly left the Oppo gathering dust, again more detail and better coherence top to bottom, but still some harshness/brightness.  (For me, one advantage of the PWD/Bridge was that it sidestepped the digital cable question, as ethernet is used to feed the DAC via the Bridge.)  Next worked on power cords and outlet - and that really helped tame some of the brightness (ended up with Cardas Clear M for DAC).  Isolating the DAC did not do much if anything.  Minimal room treatments helped, but I imagine this doesn't apply to your case bc your analog SQ is plenty pleasing.  Tried different driver tubes on amp, which also helped a little bit, maybe.  Have not tried speaker cables but after reading comment above re AQ cable now I might. 

Bottom line for me was that it took a variety of things to minimize the brightness, but in terms of equipment, getting a somewhat up-to-date DAC was the single biggest improvement from an equipment standpoint, making me believe that continuing to improve the source should be my priority. 

Luckily (or not?), I don't have a nice TT etc to compare it to, and since I was committed to digital I could justify $2000-$3000 (similar to cost of decent TT setup) for digital equipment.  Also most of the music I enjoy is available through Tidal, so I haven't had to burn too many files over to NAS.