Tried this config with and without the rx/tx gains
Tried with a SINGLE TDM400p
1.3GHz, 256Mb AMD
IDE at udma2


;
; Zapata telephony interface
;
; Configuration file

[trunkgroups]

echocancel=yes
echotraining=yes
echocancelwhenbridged=yes
usecallerid=yes
hidecallerid=no
callwaiting=yes
callwaitingcallerid=yes
usecallingpres=yes
threewaycalling=yes
transfer=yes
cancallforward=yes
callreturn=yes
callgroup=1
pickupgroup=1
callprogress=yes

; Produce a dial-tone when fxs pickup.
immediate=yes

[channels]

context=6651049         ; Incoming calls go to [clone] in extensions.conf
echocancel=yes          ; CHANNEL 1 - TOP - IRQ 10 - Clone No Bracket
echotraining=yes        ; 665-1065
echocancelwhenbridged=yes
; txgain=-6.3 the maximum function
txgain=2.0
rxgain=2.0
callprogress=no
callwaiting=yes
callwaitingcallerid=yes
busydetect=yes
signalling=fxs_ks       ; Use FXS signalling for an FXO channel
group=1
channel => 1            ; PSTN attached to port 1

context=6692862         ; Incoming calls go to [plone] in extensions.conf
echocancel=yes          ; CHANNEL 2 - MID - IRQ 9  - Clone
echotraining=yes        ; 669-2862
echocancelwhenbridged=yes
txgain=2.0
rxgain=2.0
callprogress=no
callwaiting=yes
callwaitingcallerid=yes
busydetect=yes
signalling=fxs_ks       ; Use FXS signalling for an FXO channel
group=1
channel => 2            ; PSTN attached to port 2

context=6651065         ; Incoming calls go to [dlone] in extensions.conf
echocancel=yes          ; CHANNEL 3 - BOT - IRQ 5  - Digium WildCard X101P
echotraining=yes        ; 665-1049
echocancelwhenbridged=yes
rxgain=2.0
txgain=2.0
callprogress=no
callwaiting=yes
callwaitingcallerid=yes
busydetect=yes
signalling=fxs_ks       ; Use FXS signalling for an FXO channel
group=1
channel => 3            ; PSTN attached to port 3