Changes to older system

I have experience with an NAD 3150, and some Snell EII speakers. It was a very pleasing combo, and I liked it so much that rather than sell it I gave it to close friends. They play the system daily with their LPs and CDs, and I have somewhat regular visiting privileges.

The Snells, in spite the back firing tweeter, are placed in corners for the sake of furniture layout and owners preference. I think we used brown zip cord for speaker cables. Decent bass, not bright, and sweet vocals. It’s surprisingly good. 🥃

I suppose you play “House” music on that system @zimmer266 ?
😎

I would not do any upgrades to the current preamp and amp. It’s unlikely to make a significant difference and you will never recoup that investment. 
Best upgrade path in my opinion would be speakers. Something like the GoldenEar Triton 3 used. You would solve you brightness and bass issues.
If you don’t want to part with your current speakers consider adding a subwoofer which would fill in the missing bass and tame the treble since it most likely sticks out due to lack of bottom end extension. The challenge with adding a sub is properly integrating it.

I wouldn’t worry about cables. Monster cables are not great but they’re not your problem.

Also consider adding some room treatment. GIK Acoustics make good panels and they’re not expensive. You can upgrade speakers and get few panels and stay within your $2,000 budget.

@ghdprentice recommendation of tube preamp is also a good approach. You can pick up a used Rogue RP-1 preamp for around $1,000. Combine that with a sub as it has 2 pairs of RCA outs one of which you can use to drive the sub

Good luck!

@ideal8592 You state that you have a budget of 2K per component. I assume that you are planning on replacing the entire system. If this is not true please advise.

Given my assumption is correct,  I would 1st find a pair of speakers that meet your criterion regarding tonal balance and plays well in your room. I would then consider the purchase of an integrated amplifier that mates well with said speakers. Your budget would support 4K for speakers and 3K for the integrated. 

If I am not mistaken your Cambridge CNX is a streamer/DAC. You might research AG threads on Streamers and DACs then post another AG thread under Digital regarding an up grade to your source. 

It is a process. Take your time and enjoy the journey. 

Forgot to add, use your existing cables as a baseline. You can explore upgrades there with the new system.