AMEX has been very difficult to process for sometime due to it being coded and to AMEX themselves taking a very anti-gambling view. It has been literally years since AMEX was widely available.
Also, the processing fees to the merchant (aka book or casino) are astonomically high - much higher than Neteller or CC.
Sadly, bigtimer, I don't see this situation changing anytime soon. I strongly suggest that you find an alternative method of funding your accounts - InstaCash from Neteller has certain advantages at the moment.