The difference you’re experiencing between the OPN and the KS7 is probably from the fundamental differences in the 2 platforms as explained by Um_bongo earlier. The KS7 is based on a destination specific directional platform, while the OPN is on the “open” paradigm platform. What this means is that, if you’re using the directional beam forming noise reduction program of the KS7, it’ll focus (beam form) on the sound in front of you while not picking up other surrounding sounds around you. The OPN, on the other hand, will pick up all the sounds around you, analyze, balance and apply noise reduction to speech only. That explains why you hear more with the OPN, like the AC running, etc, and less with the KS7.
Is that necessary to hear more? You be the judge. Sometime it’s good to hear more (like if you have multiple speakers around you), sometimes it’s not, depending on what you do want and don’t want to hear.
You can try to mimic the OPN more closely if you set the KS7 to music mode, or avoid the directional beam forming noise reduction mode. In the music mode, the KS7 will avoid doing special processing (like directional beam forming) and let you hear everything. But the difference if you’re in the KS7 music mode is that you’ll hear everything “unprocessed”, while with the OPN, you’ll hear everything, but all signals will be processed (analyzed, balance, then noise removed for speech) for optimal results.
I think if you’re price sensitive, the KS7 is a much better value for the money than the OPN. Sure, you may like the OPN better, but if you’re still very happy with the KS7, why spend more for the OPN, right?