Getting the right tubes to suit your musical taste is a key factor with this little box - tubes can make the difference between a very musical presentation, or being too analytical
Unfortunately My days using tubes are not even in the rear view mirror any longer, so I cannot remember which brand of tubes were best
Here’s a link that lists several brands
www.thetubestore.com - 12AX7 / ECC83 / CV4004 Tube Types
But I would start another thread pertaining to the 12AX7 specificaly and get peoples thoughts on the musical qualities of each brand.
Also, DO NOT be guided by price because there are some very good tube brands that are in the affordable end of the spectrum
Upgrading the power supply will make a difference, but I think getting the right tubes might be a more satisfying solution. Once you have the right sound you culd try upgrading the power supply
Regards - Steve