Hi Dave

Over the years (IIRC), the available DSP range has been:

DSP 33 > 5000> 5500 > 6000

Then 33 > 5000 > 5500 > 6000 > 8000

Then 33 > 5000 > 5500 > 7000 > 8000

Then 33 > 5000 > 5200 > 5500 > 7000 > 8000

Then 3100 > 5200 > 5500 > 7200 > 8000

Then 3100 > 5200 > 7200 > 8000

The data sheets for each speaker are in Duncan's Info site, and will give you a date for when each model was released. Hope that's a help.

Cheers

George