I've never heard of anyone successfully extending (not renewing) a non-OX visa in order to get the second 5 years. I've read reports of people that tried, including bringing everything that immigration should require to do so. But they were told that it wasn't possible.
If you are going to try, the money must be in a Thai bank account, in liquid cash.
You need to go to your immigration office to ask for the specific requirements. I believe it's 3 million baht but you'll want to check for yourself what your office requires. Expect to be rejected though.
I'm assuming you're Australian. Most people just go back to Australia and get a new non-OX using money in their home bank account, since the one consulate in Australia is the only one in the world Thai allows that. So Australians are the only one who use this visa.
Because you're American, your income is irrelevant. The US embassy in Thailand does not verify income, so you cannot use that for the first annual extension. That means the only thing you can use for the first one year retirement extension is 800,000 Thai baht in a Thai bank account in your name only. Having a portfolio isn't going to help you unless you're willing to cash it all out and transfer those funds into Thailand and keep them mostly locked up, for at least 1.5 years.