Mismatched phono stage

I just learned that my preamp (which I've been using for over 10 years) came from the manufacturer set up for use with a MM cartridge. However, I've been using various MC cartridges all these years.

I'm assuming I need to either change the preamp to accommodate a MC cartridge (which is an option the manufacturer offers) or I need to buy/use a MM cartridge.

Can anyone tell me what I've been missing sonically all these years? I have to assume there's some sonic shortcoming by having a mismatched phono stage. And what is the better course of action - modify the preamp to accommodate a MC cartridge or switch to a MM cartridge with my Sota turntable? Don't yet know what the manufacturer will charge to put in a MC board.

What MC have you been using? If it's a high output MC, then it likely is a fine match with what you have. If it's a low output model, it's a wonder you managed not to realize something was wrong right away, since the output would be so low you'd have had to turn you volume control way way way up to hear much of anything, which then would sound thin and send you right back to your CD player.

You might try a relatively inexpensive quality MM cart to see for yourself what you've been missing. Maybe an Audio Technica 120E?
Currently using a high output Benz Micro MC20E. Haven't noticed anything obvious. Sounds like you feel that sending in the preamp for a MC phono stage would make little, if any, difference in sound quality of the turntable and is therefore unnecessary.
Right. The Benz high output is made for use with a MM phono stage (though at 2.2mv output it is at the low side of what you can manage with your preamp -- meaning you probably have to turn the volume control up relatively far for any given listening level, which is fine). You were correct not to hear any problem. If you want to go to a low output MC, you'll need either the MC card installed in your preamp or a step up device of some kind.
Your Benz MC20E was designed to run through a MM stage. Most high-output MC's work better that way. A typical MM stage will be set up for 47K ohm loading and a MC cartridge that calls for that loading will work well.

If you are going to the trouble of getting a MC phono stage make sure that it is adjustable for gain and loading so that you can match whatever cartridge you decide to try.
I didn't know that gain was the only issue. I don't have to crank up the volume control very much at all when I switch to phono.

That being the case, then I'll forego modding my preamp to a MC board.