Sorry about that! I forgot to mention the error and how it wasn't working. I receive a ERR_NAME_NOT_RESOLVED error code when browsing in Google Chrome (DNS error). To me, this must mean that the request is not being any way rewritten and that the browser is looking for an A record for the subdomain.
I've tried your newly updated code (to ensure that there's not an infinite loop) and the code is not working (same error: DNS look up failed).
If it's of any further help, I am running a cPanel server (dunno if this makes things quirky).
Thanks again for your help! I appreciate it.