Loss of bass & full spectrum sound

It has been suggested to me by Ralph Karsten that the problems you describe could be the result of RFI contamination of your environment. The only part of your story that gives me pause is that the problem seems to show up after warm up. I don't see a tie in between that and RFI infiltration. However, I believe you stated that you live in an apartment which could surely be awash in RFI based on poulation density and neighbors using all kinds of computers/electronics with SMPS, etc.

I just wonder if there is any chance you might have a failing powwr supply capacitor in amp or source that begins to fail after a period of usage/warmup. I'm by no means a "tech" guy but it sounds like you are losing drive.

My Amp is Brand new(Musical Fidelity M6i) after replacing a privious brand new amp (Bryston B135).
It's unlikely the power supply capacitor is failing in my amp.
What you said about RFI is worth investgating
My prior statement that the system changes when warmed up was not accurate..
There is no reoccuring pattern when the sound will changes.
The kick drum & heft behind the bass lasts up to 72 hrs.

Has anyone tried Highwire powerwraps to rid RFI interference?

http://www.musicdirect.com/p-7195-highwire-all-clear-rfi-coils-pr.aspx

http://www.musicdirect.com/p-7194-highwire-powerwrap-ea.aspx

Clearly, no one here has had those interference issues to warrant an expenditure worthy of paying more than the cost of the ear buds Kijanki is promoting on another thread. I bought two pair. Problem solved.

A few suggestions:

1.
Use 10 gauge or 8 gauge speaker wire. Get the Belden 5T00UP (10awg) or the Canare Star Quad 4S11 (8awg). The thicker cable will offer less resistance than similarly designed smaller gauge cable. In my experience, I get deeper bass with the larger gauge cables. If you're bi-wiring, get a pair of speaker cables per speaker, even if you get the Canare 4S11.

2.
If you have a source with Balanced output, use it instead of RCA.

3.
Get to audition an isolation transformer type of power conditioner, such as Torus Power or Bryston BIT units.

I'm also in Manhattan and I have experienced something similar some years ago with another system. I did some experimentation a few years back looking into the effect of speaker wire gauge and bass response. Using cheap speaker wire, I found out that as the wire got bigger (smaller gauge), I got deeper bass and a more balanced sound.

Also, in my system, I get better bass response using copper wire instead of silver. Silver provides better definition, but I get a more balanced sound from top to bottom using copper-based cables.

I hope this helps.