The OpenPort 2.0 can be used to flash the series 1 RX8. I know of a few options.
MazdaEdit
http://www.epifansoft.com/mazdaEdit-versions-prices.htmlMMCFlash
http://mmcflash.ru/Mazda's own MMP
https://www.mazdaserviceinfo.com/ I guess MMP is the cheapest, as you can get it with a 72 hour subscription, but I'm not sure you can use it to flash a custom ROM -- looks like some reverse engineering would be needed. MMCFlash is just flashing software, while MazdaEdit provides an editor.
The ROMs disassemble the same way as other SH7055, but Mazda uses lots of FPU instructions so you may need to select SH4 as the proc type in Ida Pro, depending on which version you have. Version 6.1 does a good job with the ROMs I've seen OOTB. I suggest getting these register descriptions
http://www.romraider.com/forum/viewtopic.php?f=25&t=5825The RAM area is "0xFFFF6000 and Length is 0x7FFF"
If you download a trial of EcuEdit, it can locate most of the tables. You just have to point it to the start of the data section.
I see EcuFlash has an AUD mode? I don't know how that works, but the AUD pins are nicely layed out on the PCB. *shrug* Maybe that would be the free option.