[Jon]

1) While primary domain I find is usually better, using a primary domain or subdomain does depend on the given circumstances. Since you are established on the store subdomain I probably wouldn't recommend changing it at this point.

2) CDSEO only provides CDSEO information for the primary language (it does state this on the CDSEO details page).

X-Cart's never get indexed well for secondary languages because the urls are the same for each language.

Typically what I suggest for multi-lingual stores is to disable CDSEO by modifying cdseo_config.php to not include the outputfilter using an if ($store_language != 'XX') statement around the include of the outputfilter. This will allow CDSEO to function for the primary language and not modify secondary languages.