Marantz PM 15S2 limited opinions

Hi, I picked up a Marantz PM 15S2 in black not long ago and am really not sure about it. It is a great amp but it seems like the upper end is really laidback. It reminds of a hi filter being on. It is there but there is not a lot of air or crispness. Leading edges are blunted. I tried a few different PC, IC and speaker cables. I swear the stock thin power cord makes it sound more lively. I had the same feeling as the PM 17 I tried and at that time a had an 8003 here and it sounded more alive but the stage was not as big.  I go and hook up my up my old NAD 7400 Monitor series receiver set up to take aftermarket PCs and with AQ jumpers and now the sound opens up.  I have owned countless amps and so on and I just think this may be to dark and smooth for me.  Again seems to be a great amp but maybe not my cup of tea.  I swear in I enjoyed the 8003 more.  Thoughts?  Thanks
Not sure this is a close comparison but some time back I took home a PM-14S1 and compared it to a Cambridge 840A; I might have the Marantz model wrong but it was a Reference unit. I really wanted to like the Marantz but to my ears on my former system the Cambridge pulled me into the music as the Marantz was too warm. I ended up buying the Cambridge.

At the time my cables were nothing special and I'd say they were on the warm side so that didn't help the Marantz. Not sure what cables you have tried but I'd suggest Clear Day Cables as they are revealing but not at all bright; they definitely aren't a warm cable. I use them and if they don't wake that Marantz up I don't know what will. I agree... a Marantz Reference piece should be great so don't give up too soon.

Also you might be surprised what a dedicated circuit and a respectable receptacle outlet can do. I'm guessing you're plugging the Marantz directly into the wall and not a power strip? If you don't have dedicated AC lines and decent receptacles the difference between PC's isn't as big. A stock thin computer PC should not outperform a good cord.

Lastly read up on the Synergistic fuse discussion on this forum. I've took the plunge and am amazed how they have improved my system. If you do try them just go directly to the Black fuses and not the Reds. I'm running the Black in my pre and sent the Reds back for Blacks for my CD. 30 day satisfaction guarantee so why not try them. Clear Day Cables have a money back guarantee as well. 

If you don't have a few hundred hours on the Marantz give it time. Possible the demo unit I took home wasn't burned in and the Cambridge was.

What's you source components and speakers. Just reread your post and see you mentioned an old NAD Monitor Series receiver. I agree the Marantz should be better. Years ago I owned the Monitor Series 1300 and 2600A. I wonder if part of it is you spent a lot of years listening to that sound and just need to give your ears a little time as well.

Give it time and experiment more. That's part of the fun of this hobby.