@trebuchet Re sub, I have not heard many subs, so don't know whether REL is much better than SVS. When I first got the REL, I could not dial it in and it sounded horrible, so the sub sat around for a year or so. Only on second attempt and playing a lot with cross over frequency and volume (a little bit also placement), could I make it enjoyable. The key is that you should not hear the sub as a distinctive element when it is on. Rather, turning it off should make your main speakers loose some bass extension. The SVS could be perfectly fine, it may just need to be adjusted.
Consider sub-bass like salt in good cooking. You don't taste salt in a dish, but the food is more bland if it is missing.
I also have a Rega, a Naia. I have no problems with single cartridge. I don't listen to older music and don't have a single mono record. I have a couple of decent carts sitting around, but have not felt the urge of switching them out. Same with previous VPI. Just ordered a Fluance RT87 for a desktop computer system. That one has detachable headshells, but the new version is not available yet (sigh).
I am a bit more into music than gear. In my book, recordings sound more different than equipment. Put a different record on, and the amount of difference in sound vastly exceeds any equipment differences. Yes, a bit tongue in cheek, but not entirely wrong either. I absolutely like decent equipment, but I am more of a set-it-and-forget-it type.