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

Maybe try Schiit Modi Multibit for only $250? I have that and top of the line Yggy and they both tend to sound more mellow and analog than my other options, also fed from an oppo 103. Use a coax cable. Still will not beat your analog. Never tried the Lexicon but I once had a very harsh Denon CD player that kept me in analog all through the 90s. Still there mostly.

gillatgh
:"@noble100,
Yes H/T setup is full blown, front, center, surrounds, sub 5.1 setup. Processor and 5 Ch 250 W amp, D class. (The Krell died)."


Hello gillatgh,

     Okay, a 5 Ch class D amp is excellent for my suggestion.  My suggestion may initially seem a bit extreme to you but it should result in an overall sound that is less harsh and bright.  Here it is:

A.  Remove your Lexicon MC12B from your system. My thinking is the  first check is to determine if the dac in this unit is the source of your brightness issue.  
B.  Substitute your Oppo 103 as your 5.1 surround processor. The Oppo 103 can decode all of the high-resolution audio codecs from Dolby and DTS, as well as uncompressed PCM found on some soundtracks.  This means you can connect most of the Oppo's surround channel outputs directly to your 5 Ch class D amp with the exception of the SW sub and the FR/FL front L/R mains outputs. 
      The Oppo uses the Cirrus Logic CS4382 dac chip to decode and output the lossless audio from its analog 7.1 Ch outputs (you'll just be connecting those for 5.1 and leave both side channels, 'SR' and 'SL', unconnected).  My thinking is that the Cirrus dac chip outputs will likely perform better than the older dac chip(s) used in the Lexicon.

The FR and FL outputs connect to the L/R rca inputs on your Rogue integrated and you use its front panel 'HT' control to choose between the 'HT/OUT' position for cd stereo music playback and the 'HT/IN' position  for ht playback.
The SBR and SBL outputs connect to your 5 Ch amp for the Surround Back L/R speakers, the SW output to your sub and the C output to your 5 Ch amp for the center ch speaker.

For video, connect an HDMI cable from your cable box to the 'HDMI INPUT' on the Oppo.  Connect another HDMI cable from the 'HDMI 2' output on the Oppo to your hdtv HDMI input. HDMI 2 will provide the best picture quality per the Oppo BDP-103 manual.
     This configuration should provide better, less harsh, sound for both cd and ht playback since the digital signals will be decoded by the Oppo's newer internal Cirrus Logic CS4382 dac chip rather then the assumed much older dac chip(s) used in the Lexicon.  
     Please try out this configuration and report back with results.

Thanks,
  Tim

@noble,
A very interesting suggestion. Also easily do-able as explained. Not really sure what it would do with sub integration but that's not the point here anyway.
I'll try this over the weekend as time permits.
Thank you for the suggestion. 

Hi gillatgh,

     Great.  If you have good results, I can explain how to configure the audio on the Oppo's on-screen audio setup menu.for 2 ch stereo playback if you play your music cds through the Oppo.  I can also explain how to integrate your sub for both music and ht playback, too.

Tim

@noble100,
That would be awesome. Much appreciated