I've heard the name Xu Kun before but I forgot exactly who he was. I haven't seen any translated SGZ biographies of him but here is his biography in de Crespigny's book:
"Xu Kun 徐琨 (d. 199); Wu. Son of Xu Zhen and Sun Jian's sister the Lady Sun II [Slick Note: making him Sun Ce's cousin?], Xu Kun held local office and was then a successful commander under his uncle Sun Jian. In 195 he followed his cousin Sun Ce across the Yangzi. On the advice of his mother he proposed hastening the attack by building rafts for the army from rushes and reeds rather than waiting for ships. The plan was carried out, the crossing was successful and, as Wu Jing returned to Yuan Shu, Xu Kun was named Administrator of Danyang.
In 197 Yuan Shu claimed the imperial title and Sun Ce broke off with him. Yuan Shu sent his cousin Yuan Yin as Administrator of Danyang, but Xu Kun drove him away. Sun Ce was becoming concerned about the number of men under Xu Kun's command, and when his uncle Wu Jing left Yuan Shu's service and came back across the Yangzi, he gave Danyang to Wu Jing. Xu Kun continued to command troops, but he now had title as a General of the Household and was probably kept at headquarters.
After Sun Quan came to power in 200, Xu Kun joined the attack which destroyed Li Shu in Lujiang in 200; he was named a general and enfeoffed as a marquis. While fighting Huang Zu, probably in the attack of 203, Xu Kun was shot by an arrow and died. One of Xu Kun's daughters, the Lady Xu V, became a favored concubine of Sun Quan."
Sorry for the late response, but to confirm, Xu Kun was indeed an importan officer of Sun Ce's. Interestingly, Crespigny seems to have made an error since prior to the biography he lists Xu Kun's death as 199. In the actual biography though, he states Xu Kun died later than that. I'm actually not sure which date is correct.