DSP on but no audio

Hello,

I have recurring problems in an installation running in a museum that opened last month in France.
I find a workaround every two days, but the problem comes back everytime; so it seems I don't aim at the source and thus need your help.

I have exactly the same collective set on 4 exactly similar machines (same sofware; Windows XP family ed.2002 SP3, same hardware). I use Max 5 runtime 5.0.7 and the integrated sound card.

Typically, the problem is that audio stops after a while, with way/no way, depending, to turn it back on.
Sounds are OK when played outside from Max, speakers are OK.
The ezdac is blue and my vu-meters light as expected, but no sound at all goes out - this definately sounds like a driver problem; do you confirm that?

Last week I found a fix consisting in selecting "another" audio driver (among ad_mme or ad_directsound). One strange thing is that, depending on the machines, the one to work was either the one or the other. (note: if I selected the wrong one, I got an "ad_mme: stopping due to error", and the ezdac set back off after a couple of sec each time I tried to put it on.)
I have to check this out, but it even seems that it's not the same everytime.

To dodge this strange behaviour, I had asio4all installed, and forced on startup the selection of ad_asio4all via "adstatus driver".

But: for a couple of days again, the audio have gone out on 2 of the 4 machines, with no reason. It just breaks after a while.
Even if forcing manually the driver with adstatus, no sound gets back.

The top cool thing is that that the musuem is 500km from here so I only can give clear and simple instructions to people there, and thus must bet carefully on the best diagnosis.

My clues are:
- on the forums, I found it may relate to an authorization problem; how could it be the same with a runtime??
- could this be that max (auto-lauched on start-up) is opened BEFORE drivers are operationnal, so that they misfunction?
I could try and delay the launch then.
- is it basically Max (my) or Windows+drivers fault? Be honest It is important at this point that I can clean myself from all the trouble seen here...

In about 8h (when the musuem closes) I can have further tests made, in particular I'd ask for a copy of all messages from the console - too bad I don't have em already.
Let me know if you already have some clues...

This is very urgent, I'd rreeeeeeeeaaally appreciate some help!
Thomas B