HDMI video out should be well within reach of a Spartan 6 FPGA. I am still in the process of readin up and figuring out. Here are some of the more interesting reads I’ve found. Some are interesting in-depth, technical details, some are stories of people that did this before.
The Hackaday link opens up different other sources and has an interesting discussion. Hamsterworks is a more in-depth technincal commentary. Xilinx, the Spartan-manufacterer, has some helpful things to say – especially on how they intended the HDMI-protocol to be implemented on their chip:
1 HDMI port?
2 HDMI ports?
2 HDMI outputs and an HDMI input?
Maybe an extra FPGA of a different type/brand?
Two outputs would be more than enough to convert the Goldfishies into full music production battlestations.