DLNA via bridged interfaces - OS X
I'm assuming that these are separate networks with their own gateway to the Internet and that the OSX box is just a computer on both LANs (It's not their gateway)?

Bridging the networks has just effectively put a link cable between the two networks. Hosts on 1.x trying to send data to 2.x will just forward the packets to their default gateway which won't know what to do with them.

You could add a 1.x alias to the media server and keep the bridge but that's quite ugly and running two LANs on top of each other is generally discouraged. In addition, if you really wanted to do this it'd make more sense to just link the two networks with a cable rather than bridge them on a host.

The ideal solution is to probably have the default gateway on each network a router capable of routing between the two. However the routers would both need an interface on their respective LAN and an interface to connect the two routers together, plus relevant routes (at the simplest a static route on each) which probably won't be possible with the equipment you have.

By far the easiest solution is to merge the networks and move 2.x stuff onto 1.x or visa-versa, which ever is the least problematic.