Insight into PNG diving, islands and the Sepik

Hey all,
Been great reading through all the posts and definitely picked up plenty of useful info and tips.
We're heading to PNG for a month in June-July and so far our trip looks like Lae-Mt Wilhelm-Goroka-Madang-Sepik River and possibly New Britain and/or Kavieng.
Heard the diving in Tufi and Milne Bay is great but a little choppy and not so good visibility at this time of year.
How is the diving and snorkelling in Madang? Are there some nice beaches off the beaten stretch?
If anyone has dived in Kimbe Bay, would be great to get some insider information about the place and the marine biodiversity?
Thanks to those who have already recommended guides and places along the Middle and Upper Sepik. We'd love to hear any other great experiences and stories along the mighty river.

Thanks loads in advance for any help,