Its impossible to quantify how much better it'll sound. 8 times better seems pretty close though.
In all seriousness, it'll be a very big upgrade if you're system's good enough to show all the differences. The Planet's a great CDP, the HDX is a few steps up in every way. If you've got the cash and appreciate the Naim sound, its a solid investment IMO. Far better than any Sonos will ever sound. And its upgradable with an external power supply. I think there's a way to control it with an iPhone/iPod Touch, but don't hold me to that.
In all seriousness, it'll be a very big upgrade if you're system's good enough to show all the differences. The Planet's a great CDP, the HDX is a few steps up in every way. If you've got the cash and appreciate the Naim sound, its a solid investment IMO. Far better than any Sonos will ever sound. And its upgradable with an external power supply. I think there's a way to control it with an iPhone/iPod Touch, but don't hold me to that.