Bridging NAD 3155 and 2155 to include a subwoofer

The only other way besides using a y adapter from the preamp,is using the speaker level connection.

You don't bridge anything. Use the 3155 to power the bookshelf speakers and your sub has a built in amp. Try the line level connection and the speaker cable connections on your sub and pick the one that sounds best. There's no reason to use the 2155.

atyourkitchendoor, I assume you know how to bridge the 3155 and 2155 to make them into 2x125W with a pair of Y adapters and connect to the super 8. With this configuration, your super 0s will be running at full range. 
the other option is using speaker level connection and high pass the super 0s.

"the other option is using speaker level connection and high pass the super 0s."

The NHT Super 8 has no high pass filter, just a pass through, so Super Zero's will still play full range.

Agree with rsv4, the 3155 alone should be fine with the Super Zero's and try the sub both ways.

Have you searched online for manuals? Even if you find a 7155 manual, that will tell you. If you can't find one, post a response, and I'll try to help. Myself and a couple of my friends owned those back in the day when they fairly new. I may need to talk with one of them to help refresh my memory.

Yes, If using birdged configuration, y adapters is the only option.