Upgrade for better redbook performance

I have a MCH music system for CD, SACD and DVD Audio. I am very satisfied with the SACD performance. The SACD sound is smooth, airy, and very transparent. DVD Audio is not the best I've heard, but it's still pretty good. Redbook CD is okay. I would like more transparency and air and silkier midrange.

My system is somewhat unconventional. I have Linn Unidisk SC driving the power amps without a separate preamp. Unidisk SC is a universal player that plays all the formats, plus it has digital inputs and outputs, analog inputs, and variable level analog output.

One popular configuration these days seems to be HDMI based universal transport combined with HDMI 1.3 processor, such as Integra DTC-9.8 or Marantz AV8003. That would also mean a significant change in my setup, as I'll be replacing both the digital front end and the preamp section. That's a lot of risk and unknowns. I don't want to compromise on SACD sound for better redbook. Also if the improvement is small enough, I'd rather keep my current Unidisk.

Another option is adding a high quality redbook only player to the system. I can connect the redbook player to the analog input of Unidisk SC. The Unidisk analog inputs are good, but still could be the bottleneck in the system and could obscure the detail. I do have a MCH analog preamp, McCormack MAP-1, in the closet that I'm not using right now. I can put it into the system and connect the both Unidisk SC and the new redbook player. But that means more complexity, and I need to get three more pairs of interconnects.

Third option is adding a DAC with volume control, such as Benchmark or Bel Canto. I'd be using digital out from Unidisk SC to drive the DAC. My main amp has both XLR and RCA inputs. I could connect Unidisk using RCA and the DAC using XLR and switch the source without a separate preamp.

What do you think?
Without getting into the minutae of your system, the SC has pretty good Redbook and you may just be hearing the limitations of the CD format. Before spending thousands, I think you should take your SC to a dealer and do an A/B against a potential DAC or RB player. Or, at least have a friend bring over another CD player to try in your system.
I suggest you try the Benchmark DAC-1. Go to Benchmark's website and follow the links to Robert Greene's recent comments in Absolute Sound (he reviewed the new DAC/PRE but comments along the way on the DAC-1). Benchmark is currently offering a 30-day in-home trial period -- if you don't like it, you get a full refund. If you search the Audiogon forums, you will find various people commenting on the Benchmark's "dry" or "overly detailed" sound -- though some are simply repeating hearsay and do not own a DAC-1. I own one and, at least in my system, it has proven musical, transparent, and detailed in a good way -- not etched or tizzy, but allowing insights into what's in the recording. (I'm not a dealer or affiliated with Benchmark in any way -- just a longtime listener who has gone thru lots of equipment and found a keeper in the Benchmark.)
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.