Astell Kern Jr vs Oppo HA 2

Looking for sound quality comparisons between the Astell & Kern Jr and an Oppo HA 2 headphone amp used with the last version of iPod Classic which I already own. Will not be used for travel and the Astell holds enough music for me. Current headphones are Sennheiser HD650 but that could change.
Also interested in any other portable amps that would equal or surpass sound of the AK Jr when used with iPod Classic, similar in price to the Oppo
Just got a Pono, awesome sound in balanced mode
I purchased the basic AK with 64gb and I'm very happy with it. First time I played it in my car I nearly tossed my iPod out.
I've just purchased an Olive 03hd thing to see how that integrates into my home set up.