asterisk users - Jun 2006 - SpanDSP and analog Digium channels (TDM400P)

Hi

I am trying to use Asterisk as a backend to send and receive faxes over 
analog channels connected to a Siemens HiPath 3550 switch and a TDM400P 
card.
Receiving faxes, including multipage ones, works really fine, we have no 
issues at all. But when it comes to send faxes using the app_txfax 
application, spandsp can't send multipage TIFF files for some reason, it 
stops sending in the middle or end of the first page. To isolate the 
problem, I have tested sending faxes with two different fax machines 
over the same analog channels, and they work 100%, so I don't think it 
is an issue with the switch settings. I have also measured the optimal 
settings for TX and RX gain for the zaptel side, and tried many 
different levels without success. I have disabled echo cancelling too.
Now I am stuck in a dilemma, whether it is an issue with spandsp itself 
or zaptel affecting the audio transmission and consequently the 
transmitted FAX frames.
My question is, have anyone tested sending multipage faxes using spandsp 
with analog zaptel channels ? If so, is there anything that I should be 
aware of to fix this issue ?
I'm currently using libtiff 3.8.2 (but tested without success with 3.7.1 
and 3.8.0 too), spandsp 0.0.2pre26 (tested with pre23 and pre25 with 
same results), zaptel 1.2.5 and asterisk 1.2.7.1.

Thanks in advance for your time.

Regards,

Raul