Frank.. I highly recommend booking with TAs. The cruise lines are basically selling direct to you at "retail". They are NOT discounting the price to you based on what they would otherwise being to an agent for commissions.
The agents can get the exact same price, which includes their commissons. MOST are willing to discount their commission portion some, in order to offer you a lower price, and get your business.
With a group the travel agent should also be able to negotiate some perks for your group, if it's large enough. Champagne in the cabin, cocktail party or similar.
It is also quite possible to book directly with Carnival, then shop your bookings amongst TAs to find a better price, and simply have Carnival transfer your bookings to the TA. Carnival does not mind doing this at all.