BTR5 for hd599 or FiiO FH3

I got my HD 599 a bit under a month ago upgrading from hyper X cloud ii and loved the bigger sound stage and amazing imaging and have just been using on my onboard audio (strix b350-f) and my galaxy S10 and want to know if I should get the BTR5 amp for it now if that would make a noticeable difference or if I should try out some good IEM’s which should work fine on the low power amp in my phone. I will probably still end up getting both in the future but would just like to know which would be better to get first. They are fairly similar in price as well with the BTR5 being about $25 AUD more.

I would recommend buying the BTR5 first.
There should be no problems with the 50 ohms.
Then you can buy the FH3 and also operate it with the BTR5.
With the BTR5, my FH3 sound much better than directly from the phone.
However, my phone isn’t very good at audio either.

If you need something that isolates, so doesn’t leak sound and makes sure you don’t hear anything external, get the FH3. If you don’t need that, I’d probably get the BTR5 first.