Your dealer doesn't know the system or equipment, Nisrani, and I can well understand why you are confused.
If you look at thavn's post above, or kawo's following concerning wrong dealer setup procedures, then you get an idea as to what you should do.
You want to listen to the BL5s, with the subwoofer signal actually being sent to the BL5s. Look at Kawo's post for the possible problem. The BL2 can be attached, if you want to compare the sub signal of that to the BL5. But it is essential that your dealer goes into the Loudspeaker setup menu and actually disables the Lab 2. If not, the sub signal won't go to the BL5s.
Show the dealer this thread.
It's a shame that you should have this much bother in making a decision.
Cheers!