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  OP, If you are interested in hearing an all digital system, for comparative reasons, feel free to reach out via PM. I live close to you.
The damage has already been done by the time the signal gets to the DAC. The problems all occur in the nanosecond period of time it takes the laser to read the data. The system doesn’t recover no matter what you do downstream. Sorry to burst anyone’s bubble.
Thanks for all the suggestions and replies. Everything is useful.
Millercarbon- interesting suggestions I like them. Fwiw sold my R2R, Pioneer RT909 a couple years ago but still have 2 Hifi VCRS in the storage closet a brand new never used Sony and a Hitachi DVD/vhs recorder also barely used and lots of blank tapes. This sounds feasible to try. Thanks. PS I think that alone qualifies me as audiophile LOL.
To explain, my systems are totally seperate but share the Oppo as a source. Digital connection to the H/T (Lexicon) and analog connection to the Rogue.
I’m very satisfied with the AQ cabling for their resolution qualities. Could the Oppo D/A converter be the issue as it’s really the only common denominator between the 2 preamps/processors?
All suggestions will be taken into account less geo’s. I like his comments but don’t take him seriously.
As far as power and conditioning go, dedicated circuit straight from breaker box with 20 amp breakers 2ea circuits, upgrade outlets and Richard Grays power Co 4oos one on each circuit. Also the listening area has been acoustically treated.
Your Oppo cd p is Waaay down on the chain vs even middle 
of the road dacs ,  what is your budget ?  I have a BelCanto  dac 
that is very natural sounding, and there are some excellent 
Italian avacuum Tube dacs out there , Schitt Audio Yangs,
is alllways getting good reviews , your digital cable too can make a Big difference I have a Nordost   Heimdal-2 very good cable,
each cable to from other companies will give a different perspective as in dacs . Just like in analog ,each cartridge has its 
pros and cons.digital keeps getting better.it is now very musical if you take the time to tweak it power cords,interconnects ,even fuses count.
I think that handling your power well and a new DAC are what you need. I'm not sure how the MC 12 does with analog.

Here is my current thinking and experience on AC management:


https://inatinear.blogspot.com/2019/04/power-management-for-frugal-audiophiles.html

Best,
E