When I owned a pair of 501's I had them paired up with a ARC REF3 pre which I currently still use today, connection was via balanced IC's. Great combo!
I was at someones home a few years ago now and we were comparing gear, this person had MAC amps and was comparing the MAC 1000 pre, I brought over my ARC REF3 and we also compared, I preferred the MAC 1000 tube pre over all paired up with the MAC amps.
So it is really going to come down to a personal taste but at the same time be impacted with the rest of your components, speakers, cables etc.
I was at someones home a few years ago now and we were comparing gear, this person had MAC amps and was comparing the MAC 1000 pre, I brought over my ARC REF3 and we also compared, I preferred the MAC 1000 tube pre over all paired up with the MAC amps.
So it is really going to come down to a personal taste but at the same time be impacted with the rest of your components, speakers, cables etc.