The reason for the one way audio is your UDP traffic is getting blocked.
The PIX will support a 3300 in server mode,It is a bit involved to setup if you have no previous experience. The pix works by having a security levels on the interfaces and by default only permits traffic from a higher security level to lower, the inside (LAN) is 100 , the outside (internet) is 0 and the DMZ is 50, so the outside can't get to the DMZ or inside without permission and the DMZ can't get to the inside without permission. So with your server on the DMZ it is not going to be able to initiate any communication with the ICP on the inside without you putting a access-list on the inside interface permitting it.
Basically if the PIX is doing the Natting you need...
static (inside,DMZ) x.x.x.x y.y.y.y netmask 255.255.255.255
the x.x.x.x = the IP address of the server on the DMZ
the y.y.y.y = the IP address of the dedicated Public IP address on the outside interface you are going allocate for the teleworker.
On the access-list that should have been setup inbound on the PIX's outside interface (i'll call it NAME) you need...
access-list NAME extended permit tcp any host y.y.y.y eq 6800
access-list NAME extended permit tcp any host y.y.y.y eq 6801
access-list NAME extended permit udp any host y.y.y.y gt 1999
On an access-list setup outbound on the inside interface (i'll call it NAME2) you need...
access-list NAME2 extended permit tcp host x.x.x.x host z.z.z.z eq 6800
access-list NAME2 extended permit tcp host x.x.x.x host z.z.z.z eq 6801
access-list NAME2 extended permit tcp host x.x.x.x host z.z.z.z eq 6802
access-list NAME2 extended permit udp host x.x.x.x host z.z.z.z gt 1023
the z.z.z.z = the IP address of the ICP on the LAN
As you can see it can get a bit involved, if you post the PIX's config i can give you more accurate advice.