Kevin Gilmore (GSX/Dynalo etc designer) holds the Master 5/6/8/9 in extremely high regard. He said he couldn't even AFFORD to purchase the bare parts of the M8 for $1500-let alone SELL it for that. The price difference comes down to two things-being made in China, and the chassis/aesthetics of the Usa-made GSX is surely a fair cost higher. And-we don't know the exact margins-but I'd wager Kingwa, especially with his mass market approach, and huge catalog-nets an extremely small margin-surely less than Justin.
Sonically-they are both classified as being wire with gain, extremely neutral (I'd argue the M8 is more neutral). If that's the case (I believe it is based on impressions, and my own Master 8 experience)-then for all intents and purposes they sound pretty darn similar. Dubstep Girl recently made some of the same comparison impressions of the her own GSXII w/ the M8 she just heard at the ChiUnifi meet:http://www.head-fi.org/t/688561/chiunifi-7-5-november-2-2013#post_9945375.
Also, a few reasons why people go for the GSX over the Master 8/9:
1.) Aesthetics/bragging rights (big Headamp hype on this site-gorgeous build)
2.) Made in the USA vs. made in China (go figure-plus warranty shipping issues is a factor)
3.) Some anti-AGD lately on this site (imo)-people upset Kingwa releases a new product at least once per month etc)
4.) More GSX/Dynalo etc in the wild than M8's-by a fair margin. Snowball effect from this-magnified by above stated reasons.
Edited by BournePerfect - 11/26/13 at 8:21pm