Might want to look here.
The MC cartridge phono amp/or step-up is required whether you do anything with a subwoofer or not.
You are not doing justice to your system by using such a low gain on the phono.
Some people prefer electronic phono "head amplifiers" to provide the added gain. Some people prefer using a step-up transformer to do it.
Personally, I prefer the step-up transformer, as I think it provides a better load for the cartridge to drive. In any case you'll need at least a 20db gain increase.
Some options might be:
Bent Audio Mu step-up transformers - ~$800
K&K Lundahl step-up transformers - ~$250-$300
Denon Head amp (used) - perhaps around $100
Of course there are other options, those are just a few.
Get a decent step-up transformer. I got a pretty decent Ortofon T-20 Mk II used here on 'Agon a little while ago for use with my Kontrapunkt B and Audio Research PH-3 and I know have enough gain not to put the volume level way way up and not to have the noise that was present before. How you introduce subs into this issue is one the wackier angles I have seen of late.
And, oh, the single most important part of vinyl is the record itself. Even new, most are noisy and a good number are good for the garbage bin from the get go. Watch the fur fly. The truth hurts, I guess...
You are lucky to have a "Loudness" control on your amp. It is working properly, as you describe it. This is essential if you ever listen at low volume. However, it does require that the regular volume control be in a normal range, not cranked up all the way.
The easy, and completely satisfactory fix is to get a stepup transformer.
Check out the line of Audio Note transformers. They have excellent products. The used vintage Kondo transformers are simply the best but at 3000 used it should be.
check out the AN trannies at:
The ANS2 looks like a candidate and has useful adjustments for cartridges with different specifications.