First, let me say I am brand new to the whole audiophile world. I've owned the HifiMan 400i's for a long time and have always simply used them with the jack on my iPhone or computer. But recently, for some reason (lockdown fever?), the HiFi bug has got me under its spell and I've been buying stuff like crazy. Most of it isn't here yet and even if it was I'm not sure if my ears are keen enough to be a real judge. Having said that, and being fully prepared to get flamed as an ignorant newbie, here are some thoughts that might be a little out of the box.
1) Just got the HifiMan Ananda's yesterday and they blow the 400i's out of the water. I wish I had the Sundara's to compare the two.
2) The FiiO BTR5 headphone DAC/Amp/Bluetooth receiver makes quite a bit of difference streaming bluetooth from an iPhone vs playing from an iPhone jack. That difference is even larger if you use the USB DAC with a PC. I haven't been able to make the DAC work with the iPhone or an old Kindle Fire 8. Buying a Fire 10 HD to see if that works. Nice purchase for $100. I've been using Amazon Music HD as my source.
3) Just for yucks I bought the Douk P1 for $100. It came today. That little device actually checks all your boxes. Bluetooth, USB, and RCA inputs and headphone and RCA outputs.
https://www.amazon.com/Bluetooth-Preamplifier-Headphone-Amplifier-Audio/dp/B07TJS2DBT/
So far all I can say is that all the functions work and it sounds at least OK, but there is a low level of hiss in quiet passages like Perfume Genius's Moonbend. Not noticeable unless the music is dead quiet. It could be that goes away with burn in or a better DC power supply. The stock tubes aren't supposed to be the best so I bought two others that I get to play with over time. Honestly, just for entertainment value testing the tubes it might be worth the $100. I haven't done a comparison yet with the BTR5.
Probably you are better off sticking with the Schitt Vali or similar and paying more but I like playing with new toys as much as listening to the highest quality music.
1) Just got the HifiMan Ananda's yesterday and they blow the 400i's out of the water. I wish I had the Sundara's to compare the two.
2) The FiiO BTR5 headphone DAC/Amp/Bluetooth receiver makes quite a bit of difference streaming bluetooth from an iPhone vs playing from an iPhone jack. That difference is even larger if you use the USB DAC with a PC. I haven't been able to make the DAC work with the iPhone or an old Kindle Fire 8. Buying a Fire 10 HD to see if that works. Nice purchase for $100. I've been using Amazon Music HD as my source.
3) Just for yucks I bought the Douk P1 for $100. It came today. That little device actually checks all your boxes. Bluetooth, USB, and RCA inputs and headphone and RCA outputs.
https://www.amazon.com/Bluetooth-Preamplifier-Headphone-Amplifier-Audio/dp/B07TJS2DBT/
So far all I can say is that all the functions work and it sounds at least OK, but there is a low level of hiss in quiet passages like Perfume Genius's Moonbend. Not noticeable unless the music is dead quiet. It could be that goes away with burn in or a better DC power supply. The stock tubes aren't supposed to be the best so I bought two others that I get to play with over time. Honestly, just for entertainment value testing the tubes it might be worth the $100. I haven't done a comparison yet with the BTR5.
Probably you are better off sticking with the Schitt Vali or similar and paying more but I like playing with new toys as much as listening to the highest quality music.