RCA is loose

Wonderful, except for being loose. Carefully crimp it tighter. 

The end doesn't have any cuts in it. It is solid circle so it doesn't appear to have any ability to crimp.  Should have said that earlier...

jh

Use a quality adapter like an Audioquest.

Make a shim out of Teflon plumber's tape.

Fold the tape over itself multiple times and then twist it into a tight/thin string.

Place one end of the string to the inside of the male RCA and then connect it, cutting off any excess.

The slightly reduced contact area should not be a problem (might even sound better;-).

DeKay

I would try MC’s suggestion, but anyway to keep the center contact from moving will work fine.

BNC connectors make a solid connection, and you can find them here on Audiogon. 

Either buy a higher quality RCA cable with better gripping ability, or purchase a true BNC to BNC cable that uses no adapters. 

Pasternack BNC Male to BNC Male Cable Assemblies

Don't use RCAs.  They are crummy non-audio standard.

@clearthinker Can you explain this. When I connect any of my 3 amps to the pre using XLR connectors there is an audible hiss through either Elac bookshelf speakers or ML electrostatics. When I use RCAs dead silence. So how is this crummy non audio standard? I know recording studios favour XLRs but they use long runs of cable and don't give a fig about extraneous speaker noise as their only concern is what goes onto the recording.

Crummy non-audio standard?? Well alrighy then.

@johnah5 

Take a pair of regular pliers and a cloth.  Wrap the cloth around the RCA and give it a gentle squeeze.  It shouldn’t take much.

All the best.

Curiousjims' suggest is the safe route, unless you've a soft touch with the pliers.  Fastest cure(s) I can agree with. 

I've XLR mixed w/RCA with no noises, so no comprendo....*shrug*  Maybe a ground gremlin in dere, somewhere...

Hey, 2 faves in the same state, love it....*G*

Dust off those subs.....;)

@johnah5 what RCA cable is it? Sure it’s not a locking typically and you just need to tighten it? 

Also, if Reymio has AES/EBU input, I’d just switch to using that instead, with something like DH Labs AES cable…will be hard to beat. 

It's a Sablon Audio Panatela digital cable. 

wonderful sounding cable 

Doesn’t look like the locking RCA type. Sorry…it’s either the pliers or the bnc adapter. Or if you can swap it to AES cable that would be the option I’d go for. 

If crimping isnt possible, try conductive copper tape around the pin.  If jerry-rigging is necessary, might as use something more conductive than aluminium mentioned in the OP.