Rega P3 and Emotiva xps-1 (MM or MC)?

I just bought a Rega P3 and hooked it up to an Emotiva XPS-1 phono stage which has provisions for the MM and MC cartridge. My Rega is fitted with an Elys 2 MM cartridge. Oddly enough, when I use the MM option on the Emotiva, the sound is quite dull and flat, but when I switch to the MC option it comes to life and the sound is very wholesome. Any reason why? And is it safe to keep it on the MC option?
When I set the phono stage to MM the gains get deactivated. In other words, I cannot set them to 47 kohms as you suggested.

Understood. It’s defaulting to the MM setting.
So, the volume control is way up when set to MC. That’s normal due to the very low gain of a MC cartridge.
Sounds like it may be defective or not a very good product. Are the phono cables wired into the Rega, or can you substitute some RCA cables? Also, make sure the leads of the Elys are tightly connected.

I suggest you contact Emotiva support. Since you’re using a MM cart, it should be plug and play.

It sounds like the Emotiva is wired or labeled wrong. You should return it for a replacement !
The phono cables are wired into the Rega. The Emotiva help desk is helpless. Maybe I am just imagining. Maybe the MM sound is the true "flat" unbiased sound. It's just that I like the MC output sound better
Yes, but the MC setting is causing you run your TT at a very high level. Could be bad for your amp, and most definitely cause increased hiss and distortion.
Exchange for another unit.