Aaron, unless your 3806 doesn't put out enough power to drive your speakers to a safe volume level at your listening position(highly unlikely)there's no good reason to spend more money on yet more maximum power capacity. More isn't better if more isn't used, and unused headroom is simply that: unused.
As to a possible 9.2 setup, the additional two speakers would most likely be best used as "height" speakers situated several feet directly above the mains and which would be fed(if the receiver has the processing capability)with sound extracted from other channels which is considered to be heard best from an upward angle.
