I've been using the 6500 in a Fantasea housing for around 6mths and like you went from a Canon compact. Its a great rig, although takes some getting used to.
I started out with the kit 16-50mm, with wet lenses, worked ok, then I got myself a Tonika 10-17mm(canon fit).. and its much better, even though I had a UWL-09f wet lens on the 16-50. Also I picked up a 60mm Canon 2.8 macro which I've just started trying to play with, and that too works great. I also have the 90mm but yet to pay with it underwater. I guess the issue is you are going to a camera which needs a choice of lens to excel at either macro or wide angle, its a mind set I had to adapt to.
Also note regardless of housing, the lens costs can be 'ok' but you will need ports and rings which in some cases will cost more than the lens (for just a metal ring with no moving parts!).
The 6500 also is limited to a max 1/125 flash and 1/250 with an led flash trigger. Still not a massive issue, but very different to a compacts sync speed.
Also there is a massive difference in weight both dry and wet so you've been warned... I now need to transport it on holiday in two bags, mainly due to the ports.