I have this working with a heavily modified 2.2 - MS2 UK shop but it took quite a lot of work. It is working now on a alive site and has so far taken payments form Visa Maestro and solo cards without a problem. You do have to do a lot of comparing and add a few files and functions from 2.2 RC 2a and add a bit to the database tables i.e.
ALTER TABLE `order_status` ADD `public_flag` int(11) default '1' AFTER `orders_status_name` ;
ALTER TABLE `order_status` ADD `downloads_flag` int(11) default '0' AFTER `public_flag` ;
Just need to compare with 2.2 RC 2a tables.
You do need to sign-up with cardinalcommerce.com so you can produce the cardinal commerce Processor Id, Merchant Id and Transaction Password.
As you cannot take Amex payments through PayPal direct we have to tell customers to use ordinary PayPal for amex cards so you could do the same for Maestro cards if you did not want to go to all the trouble of the above.
Matt