Spend more money on the amp or the pre-amp?

OK lemaze .... here's another suggestion.
Use the volume control on your Rega & run it straight through an amp.
For $200-$300 dollars you can pick up a used Carver M400, or a David Hafler DH-200.
An audio steel @ twice the price & both will put the NAD to shame.
I still have an M400 on the shelf, even though I've been using a Classe' DR9 for 10-12 years.
I've kept it as a back up for when I ship the DR9 back to Classe' Audio to get recaped.

Agree with those who say "integrated" and add a further wrinkle:

The more efficient and sensitive your speakers are, the better a cheap amp is going to sound.  People with K-horns report great results from TPA3116 chip amp boards (which have volume controls); I've paired one with some 91db/1watt Dahlquist DQM 9s and while the sound could obviously be improved on, the results are super suggestive of what could be achieved in this manner.

You stereo is a system; build it like one.

 

I would speak to your local dealer and visit him. He will treat you with respect and even more respect your budget whatever that may be. Build your systems with respect. Happy listening my friend.

preamps are obsolete, just use digital volume control ;)

IMHO, the "separates are always better" mantra is at least 30 years out of date. Two advantages: 
Value for money: you're not paying for interconnects, another power cord, another chassis, and more packaging (it's amazing how much the latter two account for the wholesale price, especially at lower price levels). 
Performance: I believe that lot of what makes a system more "alive"-sounding comes from lowering the noise floor. Bad grounding and impedance mis-matches play havoc here; an integrated eliminates pre/power interaction problems by construction. 
Advantages of separates include automatically separate power supplies and easier shielding, but in my experience skilled designers can now make integrateds competitive with separates at prices well into five figures.