The capacitors on that PS Audio 200c are likely so dried out they are failing to filter out the 60hz hum coming in from the A/C. That could be why you get that hum.
I agree that the Rega is way too low power (only 60 watts?!?) for your speakers. The Focal really perform best when you have a very high current amplifier (big power supply - high power).
The Steller S300 is probably only one of two Class D amps I would even consider (if I was considering) because of the Class A input stage (the other one is Nord Acoustics). However, if you are looking for an alternative, it is going to be really hard to get a good enough integrated (or amp) at the $500-600 level.
The Parasound A23 above that George recommended could be nice, but it's only 125 watts per channel.
Couple of things come to mind. Parasound 2250v2 amplifier. Vincent SP331 amplifier (if you want a tube input stage). Both are excellent. Vincent has excellent bass response and voicing, but it does have a tube sonic signature (in case you are looking for pure solid state). Both are currently on sale at Audio Advisor for $999. Way above your budget, but these are just ideas.
If you want integrated, there are a couple of Yamaha S-801 integrateds on audiogon. It's about the same power as Parasound A23