There's no such thing as maxis modem. There's only BTU provided by TM and router provided by Maxis. I'm assuming you are talking about router provided by maxis. Yes you can connect to any lan port of it but it defeats the purpose of actually getting this router. If you really are looking for performance upgrade, replace the router.

Then you are loking to purchase a access point. Do note that most router doesn't function as access point.