NO! The guy is trying to rip you off. It does not matter what you hang off the B2 first stage. I own a B2 and hang a Sherwood Octo off of it.
Let me guess, he thinks you should buy a Z1 for $400 as your octo. Either that or he is trying to get you to look at the SS1.
My suggestion, if possible - SHOP somewhere else. Problem is if you have your heart set on a B2, there may not be another Atomic dealer close by and Atomic restricts Internet sales. Here is what I would do. Grab Atomics phone number from their web site and take your cell phone in the LDS with you. Ask him again if it is required and when he says yes, whip out your phone and call Atomic. Ask for the service department and ask THEM if it is required. When they tell you no, hand the phone over to the LDS guy and let HIM talk to them. I would also make sure I mention to Atomic the NAME and LOCATION of the dive shop trying to pull the wool over your eyes. I would do it after 9am PST time. They are in Hunnington Beach, CA.
Post back and let us know how it goes.
Michael
P.S. This is the kind of crap that is killing LDS! Not online sales!!!!!