According to their website, Sargent does not make a seat for the 919. You'd have to send in your seat, and they will replace the stock foam with their SuperCell foam. $369.95 to upgrade both front and rear foam, 31.95 to upgrade front foam only.
I'm debating on upgrading my seat as well. I use my flip out tie down hooks a lot, so that has me leaning towards the Sargent as the Corbin seats don't include those. But I know the wife would love having a backrest when she rides along, so she would prefer the Corbin.
So for solo, the Sargent, and for two-up, the Corbin. I don't want to buy two seats. If I could get a Sargent with a backrest, that would be ideal. I could send them my seat late fall when we start to see snow & ice. I wouldn't lose out on very much ride time that way. I know for you warmer weather riders who can ride all year long, sending in your seat is a deal breaker.
2006 Honda 919