Gain level on a REL sub

I have two RELs. Your problem is likely that this is not a punch and slam bass speaker. RELs are music audio system devices. That's why your getting the detail and textures of, say, bass strings or low organ notes or the skin of a bass drum.  This particular speaker was considered entry-level about 15 years ago. It's -6db at 25hz. You should be able to find a way to turn it up to a level that it creates boominess and sounds like it's stepping all over you speakers. To to that, turn the crossover all the way up to 120hz and you hi/low level control all the way up,  Should sound righteously horrible, but you'll hear it. Are you connected with the Neutrik Speakon connector? Check to make sure you haven't accidentally connected the black and yellow to the same speaker output on your amp.

Getting another REL will not give you the punch and slam. It's not how they are designed. I'd think Rythmik would be a cost effective solution for you. I've not heard one but do understand what they are designing their subs to do. I'd expect it to provide all of the punch and slam you could want, tho you will surrender some of that musicality you're appreciating. If this is a music system I'd suggest considering this as an evolution of your ear. If it's a home theater system then it's the wrong speaker. If your system does double duty then you've a priorities decision to make.

Good Luck!

I always liked the concept that you shouldn't notice the subwoofer when it's on, but will notice easily when turned off...

Is your 218 still under its trial period?

@surfcat thank you for your detailed explanation based on real life use of REL subs and it has helped me to decide whether it is even a good time to buy some new subs, or to continue to use my Paradigm’s for a bit while experimenting heavily with the settings on my kit.  My subs it seems are designed for HT but reviews say they actually are better for music than a lot of HT applications because they lack a lot of slam.  That’s OK by me as my system is used 90% of the time for music anyway, so perhaps I live with what I have and tweak.  I certainly don’t want things rumbling across the room, that is not how I listen.  Hopefully the OP gets their issue sorted out as well.

Have been through a progression on a number of different subs and several Rel models.  Totally agree with a number of posts that Rel subs are most compatible for 2 channel and not the best choice for HT.  IMO the best Rel for HT and music combined is the SE/SX series.  For my setup I have a stereo pair of Rel's for music and a JL Audio sub for HT LFE.  

Having said that, sufficient volume should not be a problem but will not sound great at max gain.  Could be an issue with a number of potential issues already mentioned?  Generally, the common mistake in setting up Rel subs is to have the X-over set too high and the gain too low.  Properly set up Rel's should add major "dynamics" to the music but be totally transparent.  Should not be boomy.  Comment above that the presence of the sub should not be obvious until you turn it off is right on.

Good luck in the quest...