i think the limitations of your 2-channel performance are primarily in the volume control performance of the Linn. if you add the very best redbook performance and still put it thru the Linn you will not gain much as the Linn has quite good redbook to begin with.
your system has a very simple elegance and likely works for you. but the next step is going to another level in a preamp (beyond the McCormack)....which would add complication assuming multi-channel and video are essential (it appears that they understandably are). having an uncompromised 2-channel and multi-channel combined is hard....i know i tried to do it last year just for multi-channel music in my room (i have a separate HT room).
adding a 2-channel DAC with volume control will maybe add a slight performance benefit but will still be quite complicated to integrate into your multi-channel output.
i think that your first step should be to see whether improving the volume control/preamp performance brings you sufficient benefit to complicate your system. one easy way to find out would be to buy a Placette RVC (passive volume control which defines tranparency) to discover what can be done. you would output the preamp out from the Unidisc into the RVC. an RVC is cheap and also has a 30 day trial.....or find one used.....they are easy to sell if it's not your cup of tea. until you hear what performance improvements you percieve from a considerably better preamp it will be a crap-shoot to add gear.
in any case; if you consider any 2-channel digital product and want top redbook and sacd performance.....the Playback Designs MPS-5 is the best i've heard....and also works as a server DAC if that is important. it's not cheap but won't break the bank either in the context of your very nice system.
your system has a very simple elegance and likely works for you. but the next step is going to another level in a preamp (beyond the McCormack)....which would add complication assuming multi-channel and video are essential (it appears that they understandably are). having an uncompromised 2-channel and multi-channel combined is hard....i know i tried to do it last year just for multi-channel music in my room (i have a separate HT room).
adding a 2-channel DAC with volume control will maybe add a slight performance benefit but will still be quite complicated to integrate into your multi-channel output.
i think that your first step should be to see whether improving the volume control/preamp performance brings you sufficient benefit to complicate your system. one easy way to find out would be to buy a Placette RVC (passive volume control which defines tranparency) to discover what can be done. you would output the preamp out from the Unidisc into the RVC. an RVC is cheap and also has a 30 day trial.....or find one used.....they are easy to sell if it's not your cup of tea. until you hear what performance improvements you percieve from a considerably better preamp it will be a crap-shoot to add gear.
in any case; if you consider any 2-channel digital product and want top redbook and sacd performance.....the Playback Designs MPS-5 is the best i've heard....and also works as a server DAC if that is important. it's not cheap but won't break the bank either in the context of your very nice system.