REL G2 or JL Audio F112 ..thoughts for 2 channel

This thread is unusually biased against REL. There are many who find REL subs to be the only choice for two channel systems sighting other powered subs as simply Home Theater accessories to be crossed over at 80 Hz. The word musical is generally associated in many REL descriptions.

I would suggest reading all the set up procedures involved with any subwoofer you're considering. There is also the option of purchasing DSPeaker along with any sub that doesn't have an auto EQ program.

In my experience any subwoofer is going to be room dependent to a degree. I was able to audition side by side the JL F 113, REL Studio III, and my Velodyne DD18. I have gone into greater detail elsewhere on this site regarding this comparison. To sum it up they are all top tier products. In the end I used the Velodyne Optimization Program to maximize integration for them all. The REL was very difficult to integrate and its performance the least musical which made it my last choice. The JL is a stellar performer but a bit to tight for my taste in my room. The Velodyne simply disappeared. Keep in mind these results are extremely subjective and confined to my room.

Since you have space issues I would suggest beginning with a small Velodyne DD10+. If you find its output unsatisfactory, which I doubt will happen, simply ad another.

The Velodyne has both a low and high pass filter that limits the low frequency going to the main speakers. They recommend this connection if the main speakers are somewhat deficient in the low mids. It requires a high level speaker connection to the subwoofer. Refer to the pdf manual for any misinformation I may have provided.

Using the Manual optimization software you can see your main speakers behavior below 200 Hz

Since you're so close to the Marchand I'd suggest trying the active crossover last.

Garebear, "There are many who find REL to be…" I can see were that might be confusing. No, I'm not one of the many.

IMO most subs can be musical if they can be properly controlled and equalized within the environment to create a seamless integration with the main speakers.