You can sign up Astro IPTV with Astro only.
Maxis can sells Astro package, but only with limited Astro package, and it's not under IPTV platform.

Since right now you're OnePrime user, what you can do it to call 123, request to detach your Maxis Fibre and phone plan (No longer under OnePrime & no longer enjoy mobile unlimited data).
With your stand alone Maxis Fibre acc, you can switch to Astro Broadband, which you can have Astro IPTV + Fibre Broadband + Postpaid