Hi 62vauxhall,
I’ll jump in since no one else has. The Sansui is held in high regard in this forum but will need an overhaul and is a pain to work on. I don’t know very much about the Kenwood 600 but, and correct me if I am wrong, it is one of the supremes and, if so, a splendid amplifier. If it is a supreme, it was highly valued by Echowars, a contributer and electronics technician who was a highly esteemed but who has disappeared from this AudioKarma. The power difference is inconsequential, the Kenwood likely will also need an overhaul but, I suspect, will be significantly easier to restore. If you can do the restoration yourself, the Sansui will be a challenge but you will have a superb amplifier. The Kenwood might be much easier to work on or have someone else work on. I have no experience with Kenwoods, however, and have no electronics knowledge. If the Kenwood is not an supreme then, if you liked it so much, it still might be better for you. Echowars was not a big fan of the AU D11 II and I believe would have favored the Kenwood supreme.
Search AK for posts on the Kenwood for other opinions. Here we can vouch for the sound quality of a restored Sansui, though the restoration is not easy. My 2 cents.
Marc