The RCA and Balanced cables used with the low level inputs sound fine but require more expensive interconnects. Most of the REL users I know who have full range main speakers follow RELs advice and use the supplied high level cables. I bought uograde high level cables for my setup when doing a two channel setup with full range mains. I am not certain I heard much if an improvement with the upgrade cables.
If you have a pair of class AB amplifiers and a single sub using the high level cable is more difficult. If you use a single stereo amp and a single or two subs itās easier.
But to tell you the truth I wouldnāt sweat it. If you are happy with where you are stay there. Not having ARC in your system means you donāt really have a concern in this case. The point of this thread is for people who have Anthem and REL gear.
FWIW, @Pandas2, I agree with Al. Try the high-level, Speakon connection and see what you think. I would abandon this approach only if you have access to a quality speaker/room correction software, like Anthemās ARC. IME, ARC is an excellent speaker (particularly subwoofers) integration tool. Many believe that DSP is anathema to Hi-Fi. Maybe that is true with more āheavy-handedā software, but I find ARC focuses on the mid-to-lower frequencies with a ālight touchā and does wonders for two channel listening (not to mention it is a killer DSP for setting up multi-channel HT layouts).
The thing about subwoofers is that the room dictates where they sound best. You will have to move your sub(s) around to find the best room response for bass, but I am all in on RELs recommendation for connecting their subs, sans a great subwoofer integration software option.