User details for Category or Board Subscriptions

From what I can see, Payal is on the right track. You would need a combination of v1 and v2 calls. (You might not need an additional v2 call. We do not yet have /subscribers/email/board functionality in v2. ) The call Payal suggested returns something like this:

<?xml version="1.0" encoding="utf-8" standalone="yes"?>
<response status="success">
  <users>
    <user type="user" href="/users/id/43">
      <id type="int">43</id>
      <registered type="boolean">false</registered>
      <deleted type="boolean">false</deleted>
      <anonymous type="boolean">false</anonymous>
      <login type="string">john_doe</login>
      <sso_id type="string">johndoe47</sso_id>
      <email type="string">john.doe@example.com</email>
      <registration_time type="date_time">2006-07-18T22:13:32+00:00</registration_time>
      <last_visit_time type="date_time">2006-08-12T11:14:04+00:00</last_visit_time>
      <average_message_rating type="float">4.6</average_message_rating>
      <average_rating type="float">3.9</average_rating>
      <banned type="boolean">false</banned>
    </user>
    <user type="user" href="/users/id/21">
      <id type="int">21</id>
      <registered type="boolean">false</registered>
      <deleted type="boolean">false</deleted>
      <anonymous type="boolean">false</anonymous>
      <login type="string">john_doe</login>
      <sso_id type="string">johndoe47</sso_id>
      <email type="string">john.doe@example.com</email>
      <registration_time type="date_time">2006-07-18T22:13:32+00:00</registration_time>
      <last_visit_time type="date_time">2006-08-12T11:14:04+00:00</last_visit_time>
      <average_message_rating type="float">4.6</average_message_rating>
      <average_rating type="float">3.9</average_rating>
      <banned type="boolean">false</banned>
    </user>
  </users>
</response>

If you need to follow up with additional user details with a v2 query, I recommend being as lean as possible in your select statement (i.e. avoid select *).