If DTS is working for you then it's a good chance everything is operating "bit perfect" but it's not a guarantee (DTS can smooth over errors). Assuming things are "bit perfect" all that's left is jitter. And both the processor and speaker should get rid of any jitter upstream. You might want to verify the Marrantz is "bit perfect" by playing a DTS CD (test samples that you can burn are on WIKI).

Also keep in mind you can be blocking stuff beyond 16bit and DTS will still play just fine. You can use the DAC resolution test to see how far beyond 16bits your getting (See Wiki). You should be able to get to 19-20bits fairly easy. If not something is not right.

Also you need to verify that Meridian isn't auto sensing PC as 24bit and bypassing resolution enhancement. I have not found a good way to verify that yet. Because SPDIF is ALWAYS "24 bit" and I don't know how Meridian senses it.

You could consider Music Server which is basically a "wireless soundcard" but that locks you out of applications like J River and Winamp (which I actually enjoy using myself at work). SqueezeBox Touch (24/96) or Transporter (super low jitter and 24/96) come to mind.

Problem with 518 is your locked into word size on your source (same problem as 568). And limited to 48khz.

I assume you have read about the +3dB Tweak and are you comparing CD wired straight to 5200's with computer on G61R or anything like that?

Everytime I've dug deep into something like this, I find a logical reason for the difference. #1 is I imagined it. #2 Volume differences #3 Computer setup problem, lots of subtle things can still be wrong when you think it's right #4 one component is diddling the bits, there is only one "bit perfect". And I think jitter is marginally audible these days and with Meridian that is especially true.

You might consider getting a TASCAM US-144 MKII. Great unit to help diagnose things and can act as an alternative SPDIF sound card you can compare to. They are fairly cheap. $122 on Amazon.

- Fiddler (IMHO)

If you think listening to music is fun, try learning an instrument.
HT: G61RSL, 4x5K, 5.5KHC, 2xSC6000, Transporter, HD621, Philips BDP7501 4K, Tivo, 65" LG OLED 4K C6
Computer: Foobar2000, 5K, Mojo, HiFiMan HE1000 V2