Regarding the s2member compatibility.
s2member is able to detect if there is another plugin trying to override the default user notification email, giving you the following warning:
Conflict warning: You have another theme or plugin installed that is preventing s2Member from controlling this aspect of your installation. When the pluggable function wp_new_user_notification() is handled by another plugin, it's not possible for s2Member to allow customization of New User Emails. This is NOT a major issue. In fact, in some cases, it might be desirable. That being said, if you DO want to use s2Member's customization of New User Emails, you will need to deactivate one plugin at a time until this conflict warning goes away.
In order to be able to use s2member's email customization, you need to set to NO the "Replace WP template" option in EZ Emails Settings page.
Hope this helps.