That PSU should definitely be sufficient then, I'm not sure what could be the problem. I haven't tried this particular combination in my A600 yet, I don't have an Indivision ECS

I hope there's nothing wrong with the Subway card.
Have you tried the Anaiis USB stack instead of Poseidon?
http://aminet.net/package/driver/other/anaiisIf not, try that and see if it finds the Subway, if you're willing to try it again.