Concerned about my cart/pre pairing

I assumed that if you are using powered subs, usually those products have built-in electronic crossovers.  I guess I also assumed that the crossover is also driving the main amplifier you use for upper frequencies.  That's very worth doing if you don't mind spending the money.  As it is, then of course your main amplifier is working full range and the power demands on it are greater than I thought.  What you say about the RP1, which I know zero about and which I cannot even find on the internet (albeit I did not look very hard), makes more sense, if the phono section is solid state.  Technically, I think you should be OK so far as driving your amplifier to power the speakers, but the proof of the pudding is in your listening.  The symptoms you describe do fit the description of a lack of adequate gain somewhere in your chain.  Maybe try to borrow a preamplifier with more overall gain from phono input to linestage output, and see what that gets you.  Or borrow a 1:20 SUT.

If you try using a SUT to solve your problem, keep in mind that you need to attach it to the moving magnet inputs of your phono stage, not the MC inputs..

@lewm, I think the OP can kill two birds with one stone by getting an active two way crossover for his subwoofers. It will cut the bass to his main speakers and add some more gain to the preamps output. 
jin78, check out MiniDSP I do believe they make such a crossover. It will improve your system performance quite a bit with less distortion in your main speakers, better subwoofer integration and more gain. 
As for as your phono stage is concerned the real limiting factor is the signal to noise ratio. If you are hearing noise I consider that to be a problem. I think it is unacceptable to hear any noise at the listening position at the highest levels you listen. If you hear noise then the solution is a quieter phono stage or a cartridge with higher output. 
Low output in a moving coil cartridge is an advantage because the coils are lighter (fewer turns) which gives better tracking and a higher resonance frequency pushing the high frequency response of the cartridge up higher. The problem is having to use a phono stage with high gain and a very low signal to noise ratio. These are obviously expensive. Moving Iron cartridges like the Grados and Soundsmiths have no such problem. With phono stages that have gain below 60 dB they are the superior choice IMHO. The are now some excellent moving magnet cartridges from Audio Technica, Clearaudio, and Goldring that have performance comparable to many moving coil cartridges if not better in some ways. I have never heard a moving coil cartridge as dynamic as the Charisma from Clearaudio. I think any of these would be a better match for your system. IMHO moving coil cartridges are over rated and over priced. The ones that I really like are $5k and over, a lot of money for a perishable item. If you check out my system you will see that it is pretty serious stuff and I am more than happy with cartridges made by any of the above, so much so that I have sold all my moving coil cartridges!

Yeah, well it’s always easy to tell someone to invest $$$ to solve a specific problem. I did suggest that an electronic crossover with a high pass filter would help, no doubt. So would a different preamp with more total gain. So would a cartridge with higher output. And so would a SUT.