I received my Asus Xonar STX yesterday. The difference is apparent but should play true to its potential after 50-100 hours of burn-in.
Go for Audioengine A5. They are really good sounding. I haven't heard Swans though.
On Techenclave , they are selling for Rs 7,200 .May i ask where did you buy STX from ? I've ordered Swans M200MKII since they are slightly better than Audioengine A5 after concluding from on several different forums.