You check-raise, and as I said you're identifying your hand as very strong and will likely not get action unless (a) someone else has a big hand too, or (b) someone else is a complete idiot.
Let's say you check-call, what's your plan for the turn considering you're out of position? Leading the flop also allows us to lead the turn without a 'suspicious' looking donkbet. Or do we check the turn again, and run a much greater risk of giving a free card (considering the action is most likely 2-3 handed at this point and there are more draws that can be completed on the river)
Your hand is so strong, you should be willing to throw chips in with little information. You almost certainly have the best hand now, and even if you don't are you more likely to realise you don't if you lead, someone in MP raises you and someone in LP comes over the top of you both than if you'd checked and just a bet and a raise had gone in afterwards?
You have almost certainly the best hand, therefore you are betting for value. By leading, you are also gaining information for later in the hand, and seizing the initiative in the hand, swelling the pot in many cases and thus gaining more potential value on later streets. If you check and it's checked around to someone in late position who leads for half the pot, what information have you gained, exactly? Is LP stealing (bad players will try this even into 6 people) or does he have top set? You will still ultimately think that your hand is best, which is exactly the situation you were in straight after the flop. Do you then check-call and invite others in and essentially create the same situation as you would have by leading (except for that fact that you don't have the initiative and thus a turn lead will look suspicious), or do you check-raise and risk shutting people with marginal hands which they may have called one bet with out?
There is also still a sizeable risk of it being checked around (you don't really gain much information in this case, either
). Many players will be afraid to bet with something like TP good kicker in a 7-way pot (I'm not going to speculate as to whether this is 'correct' play or not, but suffice to say it happens) simply because there is so much that could be out there that beats or is completely crushing them. Poor players will call bets all day long with such hands, though.