Help KEF 104/2 what amp do I need to drive them?

I recently picked up a pair of KEF 104/2's at a local sale. I have had these hooked up to a new yamaha receiver (around 100 watts)and they sound pretty decent. However, from the little information I have been able to find on these speakers it seems that they are rather picky and like a strong amp. I am trying to find an amp that will drive these to their full potential. Does anyone have any recomendations or past experience?

I am looking to spend no more than $500 on the amp right now and I am hoping to buy used. I have seen several 125 watt B&K amps online. I was also thinking about a used NAD amp. Can someone please help me out?

Thanks!

Madison