As Tod says transfer it as two 400k sums a couple of days apart (ckeck receipt of the first before transferring the second) but to be really safe I would do this after you have met the 800k for 3 months after the extension was granted
You do not do 90 day reports on a Non-O entry stamp as that only gives you 90 days in Thailand then you either leave or extend. You get a TM30 on any entry stamp but will only be needed if you are going to use Immigration services for anything such as an extension.