My MX5 in Calif. (91 silver with cloth seats) did not come with HRS. My
91 special edition Jap import here in NZ did.
I recall there is an entire wiring harness that you can purchase from
Mazda and thread through the back of the seats and under the carpet, etc
which connects to some connectors which exit under the carpet under the
seats (the latter installed in all MX5 --I think). Apparently some
people have found their cars which have the HRS have been incorrectly
connected resulting in a "mono" sound effect.
This link will give you and idea of the task ahead of you:
http://home.earthlink.net/~mndjones/miatapages/max5.htm
also the Mazda.net forums have loads of stuff on HRS and other subjects
http://forum.miata.net/cgi-bin/ultimate ... ardset=;st
art_point=;DaysPrune=
or "begin at the begin" with the Mazda.net home page and have fun
getting loads of opinions and ideas:
http://www.miata.net/index.html
- of course ask 5 people their opinion and get 10 different responses -
this includes NZ

I'll let the "experts" on the list take over and elaborate from here...
IMHO whatever you do, DO NOT buy the OME speakers from a Mazda dealer.
Get a good pair of 3 1/2" after-market speakers.
Personally, after I installed HRS in my silver MX5, I couldn't see how
anyone could ever drive with the top down without them

Also, when I had my OME speakers I had the fader switch "biased" to the
HRS. Now with my new aftermarket radio and HRS, the fader switch is
slightly "biased" to the door speakers resulting in a more "balanced"
sound with a better bass effect.
Hope this helps.
Regards
Bill