Nht 2.3 speakers

Hi ... let me see if I can help ... the 35hz to 25Khz @86db is the rating for the entire speaker .. the entire speaker requires a minimum 30w  to be driven and can handle up to 200w ... it's average impedance is 4 ohm but that will fluctuate .. so it only represents the average impedance for the entire speaker 

The 35hz is the lowest the speaker will reach down to but is a specification for the entire speaker which is rated at the speaker's -3db point

Speakers are usually rated at their -3db point because the room typically adds 3db of gain so with that speaker being rated at -3db @ 35hzs they are adding in the room gain and the measured response of the entire speaker is  flat theoretically when you take that into account for the extra 3db the room boost at the frequency added down in that region 

Again those specs are the rating for the entire speaker

The New driver are 65hz-3600hz Fs 67hz spl 96db 1/w 1/m. means that the new woofers only have a range of 65hz to 3600hz as compared to the entire speaker 's rating of 35hz to 25Khz and the 67hz FS means that the speaker is flat to 67hz in free space without the enclosure ... if that specification was to taken at the -3db point to compensate for the room gain in the cabinet it would probably be much closer to the OEM original driver ... the 96db @ 1w @1m is irrelevant unless it is in the cabinet and being controlled by the crossover ... the rest of those spec have to do with the cabinet size required and other parameters if you are designing a speaker form scratch

I think your replacement speakers will be very close to the original OEM drivers but you should replace all 4 drivers even though the two in the other cabinets are fine

Replacing all 4 old drivers with the new drivers assures you of matching sets in both speakers ... so I think the new speakers are very close and should be a close match for the original drivers ... just replace all 4 drivers in both speaker at the same time

Glad to see you understood my explanation of the difference between the speaker's total response of 35hz to 25Khz and the new drivers response of 67hz to 3600hz ... these new drivers are most likely a direct replacement for the older NHT OEM woofers and should work fine as long as you replace all 4 .. which I see you are  

The rest of those specs are really meant for someone trying to design speaker from scratch and wanting to use those drivers ... that tells them what the box size and configuration should be ... but is irrelevant to you as they are a direct replacement for yours  

Just go slow and be careful when making the swap .. do one speaker at a time removing it and laying it in front of the speaker box ... you need to note which side on the old  speaker the black wire goes to and which side the other red or white wire goes to so lay the new one next to the old one in the same orientation so you don't mix up the connection ... when reinstalling snug them up slowly and progressively .. like changing a tire on a car go in a star pattern and gently tighten up progressively  

Chances are the new drivers may be an improvement over the OEM units  ... good luck