asterisk users - Jan 2004 - TDM400P & X101P cards, echo issues?

Let me start by saying no, this is not the normal stupid echo question :)
I currently have a SIP device and an X101P, and have had the usual echo
issues and have played around with the various solutions, none of which
are quite perfect (understandably).. however, my girlfriend is a little
more picky than I am when she uses the phone, so I'm considering a Digium
TDMXXB card for the house.  My questions to everyone here are:

1) with an x101p and TDM card in the same box, have you noticed any echo
issues
2) if yes, how bad does it seem? Do the echo cancellers in zaptel/asterisk
do a good job of killing it, without causing issues?

I see the default setting for "echocancelwhenbridged" is no, which
gives
me some faith in going the TDM route instead of ATA route, but I'd like to
hear some sugguestions.

Also, I haven't been able to find any real documentation on the various
echo cancellers in zaptel.  Can anyone elaborate on the differences
between the various mechanisms? (ECHO_CAN_????)

Finally, I tried recompiling zaptel with -DAGGRESSIVE_SUPPRESSOR, but that
seems to cause more harm than good in my particular setup (if both
parties are talking at the same time, results are indeterminate).

I know echo is caused by a wide range of issues, a wide range of problems,
and everyone's experience has been different.  I'd like to get the most
feedback possible, and it would probably be better to address replies
directly to me (seamus@insomnia.org) to avoid cluttering the list unless
your answer will directly benefit us all :)

Thanks!
Pat