Thanks for the clarification. I have no experience with the Solo dB, but DAC section in the DX50 is already fantastic, so I'm not sure it would be worth it. Maybe a good single ended amp would be better for you, if you're looking for more power. Maybe some others will chime in with amp recommendations. I love my Leckerton UHA-6SMk2, but it doesn't seem to offer any real advantages sound-wise compared to using the DX90 headphone out.
Some say you need to have your whole audio chain balanced to realize the benefit of using your headphones/earphones balanced, but in my experience that is not always true. Just my opinion, but it shouldn't matter too much if the signal is balanced coming out of the DAC, or goes through a phase splitter in the amp. You may still hear an improvement using the single ended input on a balanced amp. For the RSA balanced amps I have tried (Protector and SR-71B), the sound is pretty similar running single ended or balanced, but balanced seems to generally create a wider soundstage for me. Most likely the warmer and darker RSA house sound isn't the best for my taste. I don't like dealing with my balanced cables and 4-pin XLR-to-RSA adapters, and prefer the convenience of single-ended for portability.
The DAC is also fantastic on the DX90 that's for sure haha. The Duet is most definitely technically superior, but iBasso just really knows how to create a fun sounding amp in their DX90 haha.
I'm a big fan of iems so power isnt always as necessary as overall finesse of an amp is. Thanks a lot for the input. Guess i have some homework to do haha. I still do adore the hell outta my Duet even single ended. Was just considering some options i may have.
Maybe I'll see if i can try some balanced portable amps when im back in Taiwan (there's NOTHING in saint louis )