Sorry, I forgot to address this. My brain was zonked as it was around 4am.I don't think the 2208 firmware is going to work on the 2308, or vice-versa. But who knows.
2308 firmware and BIOS will definitely work on 2208-based boards. This is what cross-flashing from IR to IT is. However, from the errors I've seen posted, I don't believe the reverse would work. You wouldn't want to anyway as 2308 cards have half the CPU and a small cache.