If it's not really about tuning or wiring. Then it belongs in here.
I just got the haltech elite 1500 ecu for my s2000 and decided to get the haltech wideband o2 sensor. S2000 with stock exhaust system is using two O2 sensors and I am using the stock exhaust. Haltech provide wideband O2 system with dual and single channel. I don't know which one I need to go for. In my perspective, I am wanna get the dual channel for future if I change to V6 or V8, but I don't know if is not good for tuning the s2000 with dual wideband O2 sensors or not compare to single channel.
you can buy the dual-channel and only use one sensor for your car it is no issue
As far as I know the S2k just uses the second O2 sensor to keep tabs emissions control/cat life feedback (correct me if I'm wrong). As Ross said you can run a single sensor off of a dual channel, and then run a single sensor giving you the option to run an o2 sensor per bank in the future, however a single collector O2 sensor and individual EGTs is my preference (well, 2 O2s and individual EGTs on a banked engine would be best in all honesty).