Since no up stepped up to help you I'll try, since I have 2- 3.5s.

Sounds to me like you are using the "add-a-lite" option, that has a un-powered wheel cart for the second light and a 3' bar between the motor cart and trolley cart. In a 6' long room, minus your hoods, you'd get about 1' or less max travel!

You want to mount your 2-600hps side by side, preferably about 1' apart. Intelli makes a mounting bar for this purpose, but you don't even need that. You can use any metal to create three brackets to bolt between them. Then just use chain on each end to connect to the powered trolley like you would one light. This should give you at least 4' of travel.

BTW: Consider mounting a fan facing down between the lights. This will move the upper part of the plants around and allow for better light penetration.

Hope thois helps ya....best of luck.