It will be beneficial if you plan in advance the primary use.
1) Is it purely for computer use? USB
2) CDP or SACD? COAX, AES, Optical
3) Blu-ray or Universal Player? HDMI
4) How many inputs do you need per input type?
There are some DACs that have better USB input than COAX and vise versa.
Then also consider the input of your tube amp as this will dictate the needed output of the DAC.
a) RCA?
b) Balanced Line?
A Third consideration is if you need volume control with remote for the DAC if your Tube Pre-amp does not have a remote.
With these three considerations, hopefully you will avoid an immediate upgrade.
ano na po ba ang okey na dac na maganda para sa tube amp.
yun po sana locally available.
salamat