Bass leaves after amp warms up?

My current system does not support headphones
I live close to Brooklyn

Mapman, why do you persist in pointing to the amp(s) as suspect when the phenomenon only occurs after a period of time? If they are not up to the task, don't you think that would be evident from the get-go?

No, not at all. And I agree with Mapman. If the ability of the amps to handle 2.7 to 4 ohm loads (at frequencies where most musical energy is concentrated) is marginal, it seems very conceivable that symptoms would not manifest themselves until internal temperatures have had time to rise, and more or less stabilize, following a cold start.

The one factor that seems to rule out the amps as being the culprits, of course, is that three different ones have been tried. However, all of them are integrated amps having specs that are not suggestive of robustness in dealing with very low impedances.

Yes, it seems improbable that three different amps would cause similar symptoms, but whatever the cause(s) of this problem may turn out to be, it seems clear at this point that they are improbable.

"“When you have eliminated all which is impossible, then whatever remains, however improbable, must be the truth.” -- Sherlock Holmes

Regards,
-- Al

Yes, maybe someone reading this in NYC area can help. If dealer is not local, it's hard to audition, for sure.

At this point, I just think the over-driven amp theory has the most evidence communicated to support it. Find one that will not break a sweat into 4 ohms or less and has plenty of gas to spare as a reference for comparison. That means on paper its specs indicate double the power into 4 ohms as eight. Its the only way to know for sure.

If there are any online sellers or vendors that offer money back satisfaction on amps that might be tried, that would provide a worthwhile option to pursue with little risk, other than shipping costs maybe. A good Class D amp might fit the bill and be practical to try due to small package and lighter weight for shipping.

A respected dealer suggested I purchase a sound level meter.
Measure a bass test one when it sounds good then again when it changed
Does this route have potential to lend "credibilty" to my claims
AP

Not only credibility, which isn't too important unless you are running for some type of award, but more importantly it might lead to a solution.

I have not read all of the posts. This has probably been addressed, but I'll risk it. When using a SPL meter as a guide once your system has 'warmed up' you just might find that by moving the listening chair (I assume you do all your critical listening from a centered seat in a close to equalateral triange) backward or forward (as little as 6" can may a huge difference in the bass) or the speakers but not so much, and take advantage of nulls or nodes caused by your room and or speaker/listening chair placement.

Just a WAG, but judging from your system photos you might yet have something to learn about set up and room acoustics. Just a guess mind you.

If you need help learning how to use a SPL meter just ask.

Good luck.