I have no experience with ibasso DAC . All I know that except DX100 dap using a beast dac chip sabre 9018 ,all dac chip they use is wolfson 8740 which is so popular and average  . On the other hand, you know ibasso's fame come from portable headamp with flixiblely opamp-rolling ability not from...

Dac only? Do you try Odac? It's cheap but SQ is excellent. Hardly to find any individual portable dac better than odac in this price range. I think you don't need to care much about all your money will go for dac not a combo dac/amp.  Most of highrated portable dac under 300 is in the package of...

I think you definitely don't need any amp for xb90. Even with clip+ the dap with low output power,they sound loudly with tons of bass hit to my ear. Put it down for 10s. I can imagine anyone want to pair them with E11 one of the most bassy amp i've ever try :D.