As far as I know, all the Linksys and Cisco VoIP products are compatible with NCH's software. If you are trying to use an analog line with Axon (i.e. need an FXO adapter), I recommend (and so does NCH) using the Linksys Sipura 3000 or 3102 FXO/FXS device.
I don't have any experience with Grandstream, so I cannot help you there.