Avalon Isis or Sonus Faber Liliam

Hi, I am familiar with these speakers (albeit not in A/B audition). What would you like to know?
They are alike in that they both offer a competent, consistent, and pleasant musical experience and different in some ways -- not least in that the Avalons cost quite a bit more. No doubt you are aware of this.
What music do you listen to, what musical qualities are you looking for; presumably you have enough room to place them in (both take up considerable real estate) and the prerequisite amplification to drive them...

Judging by your brief description alone, I would say stick to the Isis. The SF would probably be slightly more pronounced in the high frequencies and, while quick & dynamic enough, they would not be appreciably more so than your Isis; nor would the bass frequencies be improved (although SF offer a bass amplitude control button) - maybe a tad deeper.
What may be more attractive is the SF mid-range. The SF sounds silky whereas the Isis sounds accurate (that ceramic mid...); simply put, a badly recorded violin will be sonic purgatory on the Isis but only slight torture on the SF.
Overall, and considering you listen to jazz -- i.e. you need to reproduce dynamics and nuances full-range -- you are OK as is.