What do you mean by a different subnet? Are there two independent networks in the building? Subnet is usually referred to as the netmask. Most home networks are in the 192.168.x.y (with the x being a number between 0-255 and 7 between 1-254) address range, with a netmask of 255.255.255.0. Only devices with the same first three digits (in this example) can see each other without routing. If the netmask differs from this value, you have quite an exotic network and you need professional assistance.
If you are referring to a completely separate network that has a router between them (or you want to connect over the Internet), then a route must be defined on your computer and your media streaming device. You can add static routes to computers (Windows, Mac or *nix), but I doubt you can add a static route to a Bluray player or media player. This means (as Zip suggests) some internal network magic is required.
However, this forum would not be the place for seeking such advice. If it is more complicated than this, you really need expert advice. Preferably someone that can actually be present to assist. Remote network configuration is difficult at best. Interconnecting disparate networks is not a simple task, especially of the connection is via the Internet.
Good luck!

Dan
LG NANO85 4K TV, Samsung JU7100 4K TV, Sony BDP-S3500, Sharp 4K Roku TV, Insignia Roku TV, Roku Ultra, Premiere and Stick, Nvidia Shield, Yamaha RX-V583 AVR.
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