Well if you are wanting banners, I'm assuming you have added their points in, banner of ecstasy on the daemonettes unit and siren standard on the seeker unit. Drop the steed of slaanesh off of the herald and stick her in the daemonette unit. Other than that looks good.
Maybe drop the masque for another herald and then add that to the unit of seekers. Might have to shift some points around.
Would look something like this:
Herald of slaanesh steed, torment blade 120pts
Herald of slaanesh siren song, torment blade 120pts
31 x daemonettes muso, ecstasy 415pts
6 x seekers siren standard, muso 187pts
2 x fiends 110pts
1 x fiend xx pts
Kept your same basic ideas just moved some things around.