I'd pick Tritton 720's over low end Turtle Beach anytime. The 720's will give you simulated surround sound and be pretty close in sound to the Astro A40's. I have a Tritton Ax Pro headset, and if they're built anything like them, then they are a lot sturdier than lower end Turtle Beach headsets (I've used x11's, x31's, and have owned higher end x41's).
Also, HPX-1 can't be used without an Astro Mixamp (this is the setup that I currently use). For a cheaper HPX setup, you can use the HPX headset with the HPX-2 cables (Headset stays the same, the difference between 1 and 2 is the connection cable) and the SteelSeries LiveMix, but I can't comment on the sound of them.