I have a REL Stadium III and have only heard the Fathom in a dealer's HT setup. More than likely, The REL will **ultimately** integrate better with your main speakers, but the Fathom will probably work better for "plug and play" and should help improve issues with problematic room modes without resorting to acoustical room treatment.
It takes a LOT of work to get the REL located and setup right and Xti16 is correct that replacing the REL hi-level cable with a better aftermarket one (I like the Synergistic Research Tesla Rel Spec) will greatly improve its speed and transparency. The right power cord is needed too.
However, in my situation, bass traps were necessary with the REL to minimize the "slow and rich" characterisic you describe. Prior to adding the bass traps, I migrated to the REL's lowest crossover setting (A1=22hz) to minimize undesireable bass enhancement (just to get the improvement in soundstaging and ambience). With the traps in place, I can actually tune the rooms bass response surgically with the crossover settings to get significantly improved bass linearity. It was all worth it for me.
The REL will amaze you with its ability to enhance "recorded ambience". When switched off, the soundstage shrinks and the overall sound seems anemic. Don't know if the Fathom does this as well.
Bottom line: If you are open to a lot of tweaking (including acoustical room treatment), go with the REL. If not, get the Fathom.
It takes a LOT of work to get the REL located and setup right and Xti16 is correct that replacing the REL hi-level cable with a better aftermarket one (I like the Synergistic Research Tesla Rel Spec) will greatly improve its speed and transparency. The right power cord is needed too.
However, in my situation, bass traps were necessary with the REL to minimize the "slow and rich" characterisic you describe. Prior to adding the bass traps, I migrated to the REL's lowest crossover setting (A1=22hz) to minimize undesireable bass enhancement (just to get the improvement in soundstaging and ambience). With the traps in place, I can actually tune the rooms bass response surgically with the crossover settings to get significantly improved bass linearity. It was all worth it for me.
The REL will amaze you with its ability to enhance "recorded ambience". When switched off, the soundstage shrinks and the overall sound seems anemic. Don't know if the Fathom does this as well.
Bottom line: If you are open to a lot of tweaking (including acoustical room treatment), go with the REL. If not, get the Fathom.