Same here! I've stopped using H300 quite awhile ago too. Pairing with either DX50 or X5 resulted in a fatiguing experience within an hour.
For the ASG2 I've paired it with numerous sources such as DX50, X5, Cowon J3, iPhone 6+ and very soon DX90.
As for DX50 in particular, it is quite a good match. Actually ASG2 does have very good synergy with most sources. But through HO of DX50 and running SU1.3.3, it offers a more detailed listening experience. Bass does not overwhelm or bleed into any other frequencies. Mid bass is substantially reduced. But that is on the bass ports near closed. However I do find DX50 HO has a slight noise level. Background isn't as clean. But once matched with an amp such as E11K, it brings the attention to a whole new level. Much more refined sound and way way darker and black background which I enjoyed a lot. X5 on the other hand, offered a more neutral sound opposed to DX50. Bass impact and slam is still present. Vocals ain't as upfront compared to DX50 due to its portrayal of a wider soundstage. Coherence and dynamics wise I still prefer to use them with DX50+E11K. Nonetheless, X5 proves to be a good match with ASG2 as well.
I see that you have the DX90? It should be a pretty fantastic match as well. From my audition, DX90 has got better dynamics and coherence with a faster and deeper bass punch which can bring out the sleeping sub bass monster in ASG2. But soundstage wise, X5 is larger with a wider imaging than DX90. DX90 is more upfront in your face kind of sound. I'll chime in more when I test the DX90 with ASG2 tonight!
Thanks for the insight.
My DX90 is used with Fidue A83 atm, I'm trying to decide which I prefer, Alien or the iBasso.
While I can easily switch DX90 over to ASG-2 my OCD will kick in about separating my dap/iem combos, and we can't have possible hospitalization.
I'm hoping just to plant DX50 headphone out on ASG-2, knock her up to medium gain with silver cable and ride off into the sunset.
As a fail-safe solution, I'll strap Tralucent Dac/Amp One to DX50 line out.
Let me know your thoughts with DX90 though.