Advice for RCA Interconnect Upgrade?

 You have good gear.  Put the $600 towards upgraded speakers. That will give you a much more audible improvement than a $600 interconnect cable ever will. Much more than a $6000 interconnect. $600 towards room treatment will also be a much more effective way of improving sound. Good luck.

I would try Cardas Clear Reflection. They are warm. 

+2 for Triode Wire Labs cables.

Owner, Pete Grzybowski, is an electrical engineer with 30+ years of experience in power and signal transmission.  His cables are honest, musical and affordable.  They never sound hard or strident, instead they reveal the soul of the source material.  Add to this is the fact that he is one of the Good Guys in audio.  TWL cables have a 30-day 100% money back guarantee.

Oh, yeah...  jasonbourne52 is clueless.

@ghdprentice +1 on CARDAS CLEAR REFLECTION.

THE GOOD: I upgraded from an all-NORDOST FREY loom to an all-CARDAS CLEAR ICs/ CARDAS CLEAR REFLECTION speaker cables / CLEAR & CLEAR REFLECTION PC’s array….. with a significant step-up in dynamics, slam, and taming of sibilants / digital “”edge”. It was a progressive process as funds permitted : ICs first, then power cords, then the speaker cables. Each step was a further sequential audio performance step-up.

THE NOT-So-GOOD: You may have to open your wallet a bit more if you want to step-up to this model level of CARDAS interconnect cables . $600 bucks even for pre-owned regrettably may not do it.

Speaker sensitivity is 88db @ 8 ohms. The Aethos doesn’t appear to enjoy lower impedance loads. Since the speakers are modified, a mismatch between the amp and speakers may be afoot. The SVS may be dipping into lower impedance at certain frequencies. The integrated may lack the ability to provide the juice.