Airtunes behind wireless router/connecting two networks via a third

Not strictly linux specific, but I am hoping for some help/advice:

I recently added a wireless 802.11n router with gigabit LAN ports to
my home network. Since I was not able to make the thing (TRENDnet
TEW-633GR) work as a bridge, I installed it as a router on its own
little subnet (192.168.0). My desktop sits on the 10.0.0 subnet
(routed by a linux box with internet access) and I added my Airport
Express to the network created by the TEW (192.168.10). My old G4
PowerBook did not seem to like the b/g/n mixed mode of the TEW, so I
am using the AX for it and switched the TEW to n-only, which works
well for the new MacBook Pro. Sooo... to make a long story short,
everything works with the exception of Airtunes from my Desktop. I can
see the AX and the Airtunes speakers, but nothing else (no
configuration access and iTunes gives up switching to the Airtunes
speakers after a minute or so of trying).

Here is an attempt at an ASCII drawing:

(Internet)---|Linux Box|- 1 --- 10.0.0 --- 200 -|Desktop|
`- 1 --- 192.168.0 --- 2 -|TEW|- 1
--- 192.168.10 --- 200 -|AX|- 1 --- 10.0.1 --- 2 -|G4|


Further details:
o The Linux box was told to route 192.168.10 via the TEW's 192.168.0.2
IP.
o Routing for the 10.0.0 and 192.168.0 networks worked out of the box
after configuring the two virtual interfaces.
o All hosts on all networks can access the internet.
o The AX was put into the TEW's DMZ.
o Pings from the Desktop to the AX are seen on the linux box and are
logged as going in and out of the correct devices.
o The TEW's log does not show any blocked traffic to the AX
o Due to wiring limitations, it's near impossible to have the Desktop
and the AX on the same subnet

Any pointers greatly appreciated!