Interconnect suggestions for Audio Research Ref 5SE?

Even 92” center to center will help solve your problem. I was suggesting 84-86” as a starting point. Then spread them apart until you reach the best compromise. 
And don’t worry about the windows.
As it stands now, you have a problem no cable can solve. 

Lots of change going on here, may need to back up a bit, stop throwing cables at this mess and look at your setup. Go back to your base setup and work slowly forward. I do not think the issue is cables. SYNERGY... 

That’s a very familiar set of observations with the Ref 5SE, and I think you’re describing a real interaction rather than a simple “bright vs warm” cable issue.

The Ref 5SE has a lot of energy in the upper mids and presence region, especially compared to the LS-16, and that can make cables that emphasize leading edge speed or extreme HF openness sound a bit spotlighted on vocals and mic artifacts. WyWire Diamond and Valhalla both lean toward that highly resolved, fast presentation, which can be impressive but not always forgiving in this circuit.

In my experience with ARC line stages, cables that slightly relax the very top octave without softening midband texture tend to work best. When a cable sounds “recessed” or “analytical” here, it’s often because it’s controlling that energy but also overdamping the harmonic envelope — which seems to be what you’re hearing with the Frey and, to a lesser extent, the Cardas.

A few things I’d consider before chasing another cable immediately:

• Give each interconnect a full week if possible. The Ref 5SE is quite sensitive to dielectric settling and connector interfaces.
• Pay attention to grounding and connector pressure — small changes there can shift perceived brightness noticeably.
• If you’re running RCA, you may find that a well-implemented XLR reduces the “mic spotlight” effect simply by improving noise rejection and balance, even if the core tonality remains similar.

Sonically, I’d be looking for something that prioritizes midrange density and harmonic continuity rather than ultimate HF extension. Not rolled off — just less forward up top. Cables described as “neutral” can still sound lean here if they’re optimized for speed over body.

You’re on the right track by listening carefully and letting the system tell you what it needs. The Ref 5SE is capable of fantastic organic clarity, but it’s definitely cable-revealing and not shy about exposing mismatches.

Curious to hear where you land after more time with the Valhalla and the others.

So @fanotunes have you tried speaker placement changes or are you still in process of remediating this with cables?

I have moved the speakers in about 6” each and have reduced toe in. This has resulted in a more focused though somewhat crowded soundstage and doesn’t really address my concern.

I’ve concluded, for now anyway, that the cables weren’t the issue either…all the various cables did was introduce their own character and new variables…perhaps mitigating the top end but introducing other traits I haven’t been entirely satisfied with either.

Another member suggested I go back through everything. As the pre-amp is new to me, and as I did not have this issue before, I’m taking a closer look at the pre- noting the previous owner mentioned some top end brightness compared to another pre- he had on hand. I also see that neither of the tube sets that came with the pre- are from audio research. Not that tubes can’t be sourced from elsewhere, but it adds a variable right now.

Several have remarked that cables should be making only small differences. So, right now I’m going back to what I knew and liked before,.. Wywire. 
 

I’ve pulled the pre, tried to clean things up a bit more and am substituting in the other tubes to see if that does anything. Will almost certainly order a new set of tubes so can at least do away with that variable. And go from there..