Time for me to do my stuff!
All right, you need a few changes. First of all, get nine Scorpions and have the Fortune Farseer accompany THEM. That way, your armor save works out to be BETTER than that of a Terminator! They'll mow down infantry like there's no tomorrow. Needless to say, you'll want another Storm Guardian.
The Howling Banshees are pretty much fine. I see nothing wrong with them.
Fire Dragons. They'll work all right, I suppose; however, if you want a TRUE tank-killing force, use an Elites slot and get Wraithguard instead. That'll take down any tank, and look dang cool while you're at it. And get that Warlock that you'll use a Singing Spear without a Shuriken pistol; for him, there's no real point. Mount 'em in a Wave Serpent, and you're good to go. Even if you do want to keep the Fire Dragons, get a Bright Lance instead of a Starcannon. It fits with their tank destroying role better.
For the Dire Avengers, make yourself able to pay for that Singing Spear by making that Diresword a regular Power Weapon. Direswords have no real use, as Dire Avengers aren't really meant to kill the big bad toughies.
Those Storm Guardians seem... pointless, especially if you get Wraithguard instead of Fire Dragons like I proposed. I never really liked Fire Dragons, anyway.
If you eliminate those Storm Guardians, then you can afford a Wraithlord, providing a nice, juicy target to keep your Wave Serpents from destruction in the first turn if you go second.