Adding a second sub

I just tried to pull up the nhthifi link. No luck, but I did visit their current site. Again, no luck, re the products you mentioned, but they did have some sub systems which give me a fair idea of what they have.

You apparently want to have a left channel w/left channel sub and a right channel w/a right channel sub. Correct?

This is easy (or should be anyway) to do. Take your left sub line out IC from your reciever to the left sub line in on the sub and adjust the crossover and volume balance on the sub to your pleasure. Take the right sub line-out IC to your 2d sub and make your crossover and volume adjustments as identically as possible so you don't get channel imbalance.
Keep your crossover point as low as possible. Each sub may have provision for both left and right channel IC's. I believe it is safe to ignore one of them them and only use the appropriate one. These inputs are more likely than not blending anyway. But, if I'm wrong (and I'm unlikely ever wrong!) you can just add the 'Y' splitter and a second set of IC's as provided in the NHT manual, so there is nothing to be lost.

This should work but although I didn't find anything specific to your stuff on the NHT site, I did pull up the manual of the Ten sub and the diagram on it confirms (for me anyway) that my suggested hook up will work.

The 2d sub hook-up you have described does not provide for seperating the channels, you are just spreading the subs output about to smooth out bass response.

FWIW IMHO if you keep the crossover low enuf all of the sub(s) output will be monophonic, as it should be, and there will be little difference.

Bob, Thirsty93 is lucky to have someone available with your knowledge of the operation of his reveiver. I'm amazed about the operation of the LFE output. I've never had a complex receiver and this is all new to me. You can actually electronically insert a crossover into the circuit at that point. Amazing! :-) Certainly makes it simple to incorporate a sub (or 2).

Question - Do you think this method is optimum, or just more convenient? I would have have thought that sonically it might be better to take out signals from a Line Level out, run the satelites full range, and set the cross over to blend the sub with the bottom end of the satelite, thereby minimizing the effect of the subs incursion into the upper frequencies, assuming of course that the subs are being located in areas of the room to smooth out bass response etc, not necessarily in the immediate area of the satelites. And, where did you find a diagram or manual for the SA2 - I couldn't find one anywhere. Interesting........

(I would have have thought that sonically it might be better to take out signals from a Line Level out, run the satelites full range, and set the cross over to blend the sub with the bottom end of the satelite, thereby minimizing the effect of the subs incursion into the upper frequencies, assuming of course that the subs are being located in areas of the room to smooth out bass response etc, not necessarily in the immediate area of the satelites)This is how i use mine in the current config.
Are you saying it would be better to run the 1.5's as satilites?