For some reason I always thought that 34xx fw_all.bin doesn't work with 37xx bootloader (so you have to flash 34xx boot.bin at least once and make it install 34xx bootloader) even if you change HWID to 1101 in fw_all.bin. Probably I even tried doing this in the past. Alexander also confirms that this is true. That's why I'm really curious how you make it work.