I borrowed a pair of Nordost Heimdall 2 RCA's to connect my E-380 to the S5.5. I was amazed at the increased detail, clarity and speed they added to the music. The downside is that they are a bit too revealing and made the music sound a bit clinical and a tad bright. But it made it clear that I want to upgrade my RCA's if I keep the Accuphase as my preamp.
I would prefer a slightly more laid back presentation leaning to the warmer side. The Heimdall's are excellent but almost too much is coming through 😀.
I am currently using Signal Cable Analog Two Interconnects with upgraded Neutrik ProFi connectors. I really like the way they sound, they are just holding back some of the detail and dynamics. But given the choice between those and the Heimdalls I would stick with the Signal Cables. Not as detailed but easier to listen to.
Would be interested to hear what interconnects others are using.