Check this out: http://forums.x10hosting.com/news-announcements/60905-x10hosting-double-everything-special.html#post349843.
Closed as this should answer your question. If not, feel free to re-open this.
Hello,
With all of those DNS Zone Edits, I recommend getting a third part DNS editing service.
We will allow 15 max as that's the subdomain limit and these go tward your subdomain limit.
This is not a rule we can bend. If we did for you, we would for everybody. Please make it be above the page fold or think about using the Advanced plan.
Please if you have any other questions feel free to ask them.