It's about just sound if you're out for show. If it's just sound then don't read on.
A X will gain a few ponies and better ETs if done right. Seriously even if you're about sound a car made for HP will sound kick ass. Just like tuning a French horn or a speaker an exhaust uses the physic's rules of pressure waves, temperature/volume ratios and fluid dynamics. They are subject to frequency, diameters, lengths, etc just like any sound system with the addition of significant temperature differentials. The reason a X is better is it's important to know that high pitched sounds (high RPM pulses) can equalize pressure from one bank to another at low RPM but they don't like to turn the corners and run the distances that a H employs at high frequencies (high RPM). A X interleaves or "blends" the pulses for increased scavenging and does especially well at WOT/high RPM. You'll see all kinds of opinions but you won't find any exhaust tech papers that will say otherwise and if you understand sounds waves it makes sense that it works the way it does.
If you're just about sound then don't port your MAF or TB, don't put on less restrictive muffles, change pipes, use an underdrive pulley, use a TB bypass, reroute the intake or do any of the "little" things that made a performance difference. If it doesn't work for your "note' then what's the point?
What Is the Difference Between X-Pipe and H-Pipe? | eHow.com
in particular page 3