Bass leaves after amp warms up?

What is the goal of what what you are discussing?

The goal is to characterize the symptoms as precisely as possible, in technical terms. Hopefully that would help to identify or at least narrow down the possible cause(s).

Can I ask when you listen to both versions if one sounds more satisfying than the other?

Hard to say. Partly because neither sounded satisfying, due to the excessively hot treble, and to some extent also due to a general lack of transparency. I have no way of knowing, of course, the extent to which all of that may have been contributed to by the original recording, vs. your system's reproduction of it, vs. your recorder and microphone.

Also, as I indicated, precise equalization of volume levels was problematical, which further increases the difficulty of making any judgments.

Can you provide an answer to my question about whether or not your recorder applied AGC and/or peak limiting when your recordings were created? If you are not sure, let us know the make and model of the recorder. If an external microphone was used with it, let us know its make and model as well.

Regards,
-- Al

I use Marantz Professional cd recorder CDR400 w/built in mic.

AL I petitioned my dealer to lend me a dedicated 250 w amp from Musical Fidelity.
Do you feel this will resolve the problem?

http://www.musicalfidelity.com/products/m6series/m6prx/

Musical Fidelity M6 power amp to be borrowed next week

I petitioned my dealer to lend me a dedicated 250 w amp from Musical Fidelity. Do you feel this will resolve the problem?

Could be, but I'm by no means certain. I would expect it to be more capable of handling low impedances than the integrated amps you've used, but once again it unfortunately does not appear to have a 4 ohm power rating.

I use Marantz Professional cd recorder CDR400 w/built in mic.

Couldn't find any info on a Marantz CDR400, but I did find this on the CDR420. If it is the same as or similar to that model, it does provide both AGC (referred to in the writeup as ALC) and peak limiting. To obtain recordings that are as meaningful as possible for present purposes, both of those functions should be switched off, and the recording level set such that the maximum level that is reached during the track at any time (whether or not the problem is present) is several db (perhaps 6 db or so) below the 0 db reference point. All settings should then be left exactly the same for both recordings.

Regards,
-- Al