Your pain sounds more chronic than mind so it's hard to say. I never went to a doctor or chiropractor for it (I'm way too suborn for that.) My knee pain was a shooting pain that would continue after leaving the chair, at some point it became really really hard to sit in my old chair for extended time.
Most of those leg pains when sitting have to do with how high the chair goes and how the ridge at the end of the chair seat is shaped.
Back pain was standard back pain that anyone would experience if you sat in an uncomfortable chair hunched over.
I also had a lot of wrist pain because the arms on my char where way too low. Embody has adjustable arms on it so you can set it to a proper height to grip a mouse.
You might want to check out the Envelope Desk too:
Envelop Desk - Products - Herman Miller
That + an Embody you be pimping in ergonomics.
So if your asking me if you should get one, the answer is yes. That being said you have to look at your whole set up. Is your desk tall enough? No point to buy an adjustable chair when your desk is too low. So you'll probably want to look in to an adjustable desk.