What's next for the ultimate sound quality?

The question may be naive, but I'm not sure what's next to try in the quest for the ultimate sound. I owned the entry level magnepans mmg (didn't like them much for anything but jazz), monitor audio S6 (good all around, imho, but nothing spectacular except for the cheap price tag). Lately I built speakers myself that should supposedly rival the best in the world (ZRT 2.5 from Zaph Audio with Scanspeak drivers)

(design):
http://www.zaphaudio.com/ZRT.html

actual speakers:
http://picasaweb.google.com/grybkin/ZRTSpeakers

The question is what's next? These speakers use one of the best drivers in the world and the best I've heard to date with excellent bass and accurate sound, but soundstage and imaging could be improved (magnepans are better). Also, the sound is a little thin. Am I asking too much, though, from 2 wooden boxes with paper diaphragms in the middle? The speakers are built precisely up to spec and I'm pretty sure that's the way they should sound.

Have I reached the limit where the speakers should be left alone and improving other components can make better returns; e.g, room acoustics and/or amplifier not to mention using quality recordings?

P.S. The receiver I'm currently using is Panasonic SA57 connected to a computer via digital COAX cable and JULI@ sound card. Despite the cheap price, this receiver is great, imho, and sounds better than my NAD 754 (probably because Panasonic is on the bright side and the speakers are warm, so it pairs with them better).

Thanks!
Gleb.