Bridging NAD 3155 and 2155 to include a subwoofer

"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.

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

Using the 3155 and 2155 bridged is irrelevant to sub connection. It can be connected either way, line level or speaker level.

Just want to clear things up and not to offends anybody,
https://www.amazon.com/dp/B0049FGP7O?_encoding=UTF8&*Version*=1&*entries*=0&showDetailTe...
above  information shown the speaker level output on super 8 do has a built-in 100Hz high-pass filter.
If 3155 and 2155 are bridged, the amp output will be floating from ground and should not connect via speaker level input of the super 8 that has common ground on both R/L negative connections.

@imhififan

No one is offended and your additional information is appreciated. Before responding to this post, I looked at the back of the sub and there was no indication it had a high pass filter. Then I did a search for "NHT Super 8 manual". First choice was Crutchfield, nothing listed in features, download the manual, nothing there about high pass filter, although it stated for more information, see online manual at NHT.com. I go there and download, even less pages than the Crutchfield download, still nothing. So, I had to assume no high pass filter. About the bridged hookup, I apologize to you and OP, brain f**t, and just put all of that foot in my mouth.

Now, and I think you will agree, the best way to connect the OP equipment is to use the 3155 only with it’s output to "High Level In" on the Super 8, then "High Level Out" from the Super 8 to each Super Zero. Crossover set at just below 120Hz, according to the manual. The 3155 should be more than enough power for the Super Zero’s connected this way and the advantage of having them high passed far outweighs the advantage of extra power and playing them full range. Actually the overall system capability should be greater in high passed configuration since there will be much less chance to overdrive the Zero and bottom out it’s small woofer.