Separates or Integrated? What makes more sense?

Not to say there aren't some really nice integrated amps out there but in my present system my power supplies for the preamp and phono pre are separate. The makers of these probably wouldn't go to this trouble if it weren't a step up. I mean I guess they could take this approach for panache but they probably are more concerned with performance.
When you locate the power supplies in the amp box with preamp, and power amp and in some cases phono pre it would seem to present a problem with noise, something my system with high efficiency speakers is particularly sensitive to. So separates it is for me. The longer I'm in the hobby the more aware I am as to the importance of the power supplies. For the more knowledgeable designers of equipment on this forum, it would be nice to hear your honest appraisal of the significance and differences involved in isolation of the power supplies, benefits and drawbacks.

dentdog is correct. Isolating a preamp from a power amp in the form of separates will pay much greater dividends than any cable or power cord improvements. In fact to suggest otherwise, I think, shows a pretty glaring lack of knowledge regarding significant fundamentals. 

I know of no integrated amps that compare with separates made by the same company. Look to Gryphon or Vitus as examples.

I have read the entire thread and agree with most all of the posts. I typically choose separates, but my best audio buddy goes with integrateds. I do own a couple of integrated amplifiers as well.

I accompanied my wife on a business trip last week and was able to visit a high-end store in Falls Church, Virginia. I heard the $5000 Prima Luna integrated and was very impressed! It was driving a small pair of Eggleston Works floor standers which were also impressive. They also had the Luxman integrated amplifiers. First time I had seen Luxman in a store in many years. I was thrilled with the looks, build quality, fit and finish, and most importantly the sound! Both the newest versions of L509 (L-509 X) and 590 (L-590 AXII) are on my shortlist. The Luxman turntables were also very nice.

That being said, My buddy just picked up a used NAD 375BEE for under $500. I actually got it for him and delivered it to his home. We listened to it on his Focal 30th anniversary Chorus 826W ($3500 when new) speakers. I was shocked and amazed at how good it was, and how close it was to the experience I had in Virginia with the far more expensive amplifiers. Compared to his Marantz 8004 integrated, the NAD was transformative. I had always thought that the Marantz was a solid amplifier, but there was no comparison. The NAD blew it away in every area, at least with the Focal speakers and  in his room.

@dentdog ,
What if the integrated amp had a separate, dual power supply??