you won`t have to change the majority of your media for a very very long time. i set up my xp2 over a year ago and the exact same media is running in it today. sponges take forever to break down and the ceramic biomedia will last you forever. be sure to rinse your media in old tank water to preserve the bacteria!
the only part of the media that will need regular changing to new is filter floss or polyester batting. there really is no way to rinse it and replacing it is cheap and easy if you get one of the large bags of polyester batting (like the stuff you make quilts with) from walmart or some such big box store.
can`t comment on the hydroton media. never heard of it.
Gotcha,
I guess the thing I don't like about the XP3 comapred to the eheim i was looking at is the filters are on the bottom, where with the eheim if all you have to do is change the filters they are rigth on top, first thing out, so you wouldnt need to dissasemble the whole thing to change what you need.
Is this relevant or not realyl since you only do it every once in a while?