Info for the non-gamblers:-
Vegas sets the inital lines based on their predictions of what betters will justify as the median ground where they will get 50% of bets on either side of the line.
If the line is 5.5 games it's a straight up bet less the vig (juice, or bookies take). This is usually 10% and is expressed as -110. This is the initial number posted and can fluctuate in 2 ways over the course of the preseason/season.
First way is the vig can change to entice people to bet one way or another. If more people are putting money on the Fins to go over 5.5, then the bookies can increase the payout on the under by going to 100 or +110 or +120 etc. This conversely usually affects the payout on the over negatively...-120, -130 etc.
The second way, usually used when there is a large bias to one direction of betting, the line itself moves. If most of the action is on the over, then the line will move up to 6.5 and the vig will reset to -110.
The important point is the bookie always tries to balance the total dollar amount on either side of the line, that way they are guaranteed their combined vig of about 20%.
Hell of a business when you're always guaranteed to win!
FYI - I wouldn't touch this line even though I think we're going to be much better than last year. Much better doesn't necessarily equal more wins.