It depends on what you like. I’m not a fan of Sabre chips. I do have an R2R DAC. Get something that you can listen to and return if you don’t like, if that’s possible.
Don’t get anything yet until the amp and tubes are broken in otherwise you won’t know what’s what.
If you are using a stock power cord, put the money into an aftermarket power cord instead of a power conditioner.
It is sad that it's quite impossible to return stuff in my country if we don't like it. After buying HA-300, I may have enough budget to buy power cords and a small power conditioner ( like AQ Niagara 1000/1200 ) at the end of this year. I'm not in hurry to buy DAC ( probably next year ) since it's seems that DAC technology changes quite quickly ( IMHO ) . Also waiting for amp and tubes to be broken in per your suggestion is a great idea. It might have good synergy with my R-28 after stable. If you have preferred power cord, please recommend. Thank you.