The Navigator obviously is a fairly new addition to RCI I shouldn't think there would be much noise or vibration on deck 6. We generally book a later dining option, firstly because as you say there will be less children and the theatre usually perform twice every evening anyway so you won;t miss any entertainment. We are doing to same cruise in November so I hope we all have a good one, I am sure you will enjoy the cruise very muc.
I cannot be specific to that ship but you will be unlikely to feel any vibration noise on any ship's balcony cabin decks. The choice of dining time is really up to you, but we pick 2nd seating because after going on the port trips we find that early seating is too early. However, 2nd sitting means an approx. 8.30pm late eating, & we generally don't get up from the table before 10pm, which could mean going to bed very full, unless you are disco night-owls! You will also not feel like indulging much on the midnight buffets, which you may find to be OK. You will not miss out on any shows as they are mixed, either pre or post-dinner mirror-image ones.
We never hear much anyway, but if you are a light sleeper, my advice would be to take earplug as some folk moan about engine room, air con noise etc? We have been on old and new ships (5 cruises) and nothing has woke us up ever.
We have had both sittings for meals. early sitting (with out children) has advantages of seeing early show (If wanted) and then taking advantage of all the entertainemnt throughout the evening. But has disadvantage of if you book a trip for all day they don't usually get back until late, so the early sitting is a rush, however if you make your own way around you don't tend to wander around all day, so you can get ready. Also look at how many days you are at sea, because if you sunbath all day, an early sitting can be a welcomed break from a hard day in the sun. We have also dined on the late sitting. I must admit I do not like this as you miss most of the fun things i.,e. quiz, game shows (we like these)They start about 9-9.30. You also are very full and don't want to really move very far, or do a lot after. As a previous reply said you will also miss all the lovely mid night buffetts etc. In general most people who can aford the price of a RCI cruise do not have children that are allowed to run wild. I fnd most kids love the atmosphere of the glam restaurant and its plush surroundings. We went RCI in Mid May 06 and thoroughly enjoyed it. We have booked for the RCI maiden cruise of Independance of the seas in May 08, I can't wait. Don't worry about missing shows etc you can go in whichever one you want, and you can always eat elsewhere, but my advice would be to be waited on hand & foot, as we all deserve a pamper don't we. If you need anymore help mail me on firstname.lastname@example.org, I'll try and help. Also use you cruise experts at thomas cook etc, thats what they're paid for (even if not booked through them) Have a super holiday, you'll be very spoilt and become very additcted. A beach hol will never compaire now.
We used deck 8 on Navigator and never had any noise or vibration, the ship is unbelieveable, we had second sitting as all adults in our party which we prefer, the reason as when we returned from excursions it gave a bit of time to get showered and ready for the evening.