The Tell-tale sign... model 300 operates at about 390 joules, 600 signature about 470 joules.
Also, back of Sunfire Signature 600
https://www.ukaudiomart.com/details/649279940-sunfire-signature-600-ii-one-of-the-most-powerful-ampl...
https://forum.audiogon.com/discussions/sunfire-signature-what-is-this
Also, back of Sunfire Signature 600
https://www.ukaudiomart.com/details/649279940-sunfire-signature-600-ii-one-of-the-most-powerful-ampl...
https://forum.audiogon.com/discussions/sunfire-signature-what-is-this