When the sound quality is not satisfying, although the turntable is connected right, an external phono-preamp should solve this problem.
There are a lot of units on the market, up from approx. € 50,00 to "unlimited".
For my own, i've got a pro-ject Phono Box II, it's killing me with bass compared with the lousy phono-stage in my amp.
There are as well solutions with a built in analog to digital-converter (USB-Connector) what allow to digitalize/record lp's with a computer (into mp3-format, f.e.) in a relatively comfortable manner.
As your turntable is a rega, the rega fono or fono mini (with USB) maybe a nice choice.
But even with a separate phono-preamp there maybe more or less volume differences between phono and other inputs, depending on the sensitivity of the pre-amp, its output level, the output-level of the cartridge and the level of the individual record itself. This shouldn't be a problem. In my case, phono usually is a bit louder than CD/DVD, what can as well be the other way round.
One record a day keeps the doctor away!