Connect to the receiver via analog? I'm not sure I even see the point in that, because then it's going through extra analog output stages. More chances to color and distort the sound.
Connecting your headphones directly to the sound card, on the other hand...now that's more in line with buying such high-end cards in the first place.
In terms of sound quality, I don't know how much better, if any, the Essence STX actually is. For that, I'd need a card to review first. But one thing that seems to swing users in its favor is that it basically has a FiiO E9 built-in with regard to the headphone amplifier circuit. It's quite powerful and should be a good fit for your HD 650. (Then there's the usual distaste people have for Creative drivers, though I've heard my fair share of complaints about Xonar drivers too.)
On the flip side, the Titanium HD has a major edge in gaming thanks to the X-Fi DSP and Creative generally holding all sorts of gaming-related technologies with an iron grip, at least if you still play games that use either DirectSound3D or OpenAL. For games that have software-processed audio engines, EAX is a non-factor and CMSS-3D Headphone is dropped to Dolby Headphone's level of virtual 7.1, though. It also still sounds very good. As for the headphone amplifier circuit, I don't know how good or bad it is for more demanding dynamic/ortho headphones like the HD 650, but you could probably do worse.
May I ask what games you generally play most of the time? That'll help me tell how much benefit you'd get from the X-Fi cards overall.
Edited by NamelessPFG - 1/21/12 at 1:39pm