Portable DAC/amp for HD 660s2

Recently I purchased a pair of HD660s2 that I have been enjoying with the fiio btr13. After purchasing a pair of kiwi ear astrals recently, I’ve just been blown away by the difference in sound quality when using the same dac/amp. Due to the massive difference in ease of driving between the two and the difference being so marked in all regards, I’m starting to wonder if the problem lies in my dac/amp. I purchased my btr13 at Microcenter and called ahead and would be able to exchange it for the fiio btr17 this week if I want to. Would this be a good switch? Is the btr13 too weak for the HD660s2? Or do yall think I’m just experiencing a difference due to them being open back headphones vs iems. The dac/amp needs to be portable and potentially Bluetooth due to a significant portion of usage being with an iPad Pro.