Angela,
Sounds like a great adventure for you and hubby!
A buddy and I rode Cambodia a few years ago. We wanted to ride from Pnomh Penh to Siem Reap, but the rental owner talked us out of it... the road is extremely busy with truck traffic and constantly under construction. Just not enjoyable at all. We ended up riding south to Kep, which was excellent. You can also visit the killing fields in the area. I would recommend that if you want to see Angkor Wat, just fly into Siem Reap and visit, then fly out.
The best motorcycle riding I have found in all of Asia is northern Thailand. Plenty of countryside, very few crowds, and endless charming villages. The roads are excellent.
The Mae Hong Son loop is absolutely wonderful. Fly into Chiang Mai and either rent bikes or join a group there. I have a friend who operates a tour company of Chiang Mai:
Bike Tour Asia : Thailand Motorcycle Tours | SE.Asia Motorcycle Touring
Let me know if I can help further
