Have seen this Threshold SA/3 Upgrade

I just acquired a Threshold SA/3 that has a special capacitor upgrade. I am not familiar with the particular upgrade and would like to know if anyone else has seen this and let me know its specific purpose. By the way, the amp sound simply amazing.
Links to the photos:
http://postimg.org/image/crxc62du1/
http://postimg.org/image/t5hbp7tzd/
http://postimg.org/image/dl9xyojux/

Thanks