If I buy a pair of speakers with 86db (8 ohm) sensitivity as surrounds to go with fronts and a center rated at 92db (8 ohm) sensitivity can that be a problem sound wise?; or pose any other problem?

If you calibrate the system correctly I see no problems at all.

No problem. Just make sure you match the levels properly via your receivers test tones and spl meter. If you don't have one (and you really should) use your ears.

I agree with the above posts. Just calibrate your system properly and there should be no problem.

At the calibrated freq everything will be fine. You may notice some differences at really low volumes or really high ones (below/above whatever level you calibrate too). Either way I don't think it will be anything to really worry about.