Can I make the volume louder by using a pre-amp?

Are you certain the phono pre is operating aside from just being an existing input? Are there other selections that must be made, as Tls49 has pointed out?

Well I'll be hornswaggled! The inputs are in 2 separate banks. Never seen
that before! My bad.

Mofimadness, Tls49 & Mechans - thank you for the comments. I will go into the receiver setup and see if I can make those adjustments.
If the input sensitivity of the receiver is 2.5 and the output of the Dyna MC is 2.5 is there any advantage to boosting the signal between the turntable and the receiver with a preamp? Would that help at all? Is that possible?
Sorry if it is a silly question, but I don't have any experience with phono preamps and higher end phono equipment. The Rega is the first real upper end purchase I have made in the phono realm. Looking forward to finally making my old vinyl sing, and just want to make sure I am not limiting the potential with an incorrect setup, or something needed to assist my existing components limitations. Thank you.

Dkrubis...no questions are silly. You should always ask, if you don't know/understand something, than going ahead a messing things up.

First off...your AVR3808CI should be fine to use with your RP6, once we figure out the volume/gain issue.

Second...you can't really use a SUT, (or a pre-preamp) into your existing phono input because you will overload the input and cause some nasty distortion. SUT's are designed to boast a low output moving coil cartridge, (usually .3mv or lower). Your Dyna is 2.5mv, (considered a high output moving coil), so a SUT would majorly overload what you have now.

You could always buy a separate phono stage. These run into an existing high level input, (anything EXCEPT the phono input). An outboard phono stage, depending on make and model and price, could be a major step up in performance. There are many to chose from.

Bottom line is, your receiver should be fine. You can always get better sound if you want to spend the money.

Sensitivity is the lowest value that the phono input will amplify correctly. Since the cartridge also has an output of 2.5mV, that is the lowest value that will work correctly. You would have been better off with a higher output phono cartridge. The way it is now, you don't have a lot of options. A SUT will not help since you only need a step up of 1:2 or 1:3. Any more than that will overload your phono stage. I don't believe there are any SUTs in that range.