Hi Matt,
I want to clarify that whilst the suggestions above for
newer AP options that are compatible with your legacy firmware are
great, you should not expect any significant improvement in signal coverage with a
newer model of AP. The ZF7962 had powerful TX (upto 26dB), which is significantly higher than similar current APs, such as the R610 (upto 22dB).
Signal (RSSI) is largely dictated by local regulatory limitations, material attenuation and client device limitations. In indoor scenarios, most 3-stream (and above) APs can exceed regulatory limits at 2.4GHz.
I would recommend adding in additional AP(s) in the areas where you require additional coverage.
HTH,
Darrel.