A "more holographic" stage is also my experience by upgrading to Synergistic's X-series cables, although using all unbalanced interfaces. Actually only the interconnect cables & MCC-III DC control cables are installed so far, as of only about a week ago. HF & LF extension also moved up a notch or two, with an added sense of "naturalness". Just today I received the MK-III DC output shielding modules for the Master Control Center, upgrading it from MK-II to MK-III (when I do actually install them). That will finally complete the X-series upgrade.
Regarding the C275, Blue this preamp is absolutely fantastic & it's not even the latest "C275 V" model. It is an internally unbalanced design (that's OK - most of my equipment is single ended anyway) but it has two channels of balanced line receivers 'tacked on' at the input & two channels of balanced output line driver modules, none of which I've ever used. I also have the internal phono stage which is very good, nice & quiet, high gain, but cartridge-loading options are somewhat limited & Axxis/Accuphase won't provide me a schematic so that I can modify the loading terminations myself, which I'm ticked at them about "being difficult" in that regard. I'm going to go into it anyway after the warranty expires. But the preamp is so completely fully featured & I'm very satisfied nevertheless. Every control feature that my heart desires is included, even has tone & loudness controls for Eq & low-level late night listening, tone-bypass, phase inversion, headphone amp, monitor loops, mono mode, mute mode, remote control of volume & source-selector, and the gold anodized face is a work of art just like the P450 with its big beautifully backlit metering. I went through a lot of equipment trades getting to this point, but when I finally got this stuff I stopped trading, it is just SO GOOD. The C290 I can't even imagine, but it's fully balanced & so the C275 is actually the best fit of their line for my purposes, & actually is the P450's intended mate. For AC cords I use the Synergistic Designer Reference Squared's on both components, also just upgraded to X-series.
Click on my username & scroll down to my Bio if you want to see the complete system description, it's all shown there.