Rectifier Tube Clarification/Help W/ Dared 2000a

So after a bit of research I've made the plunge into the world of tube amplification and purchased a Dared SL-2000A based on price-point and positive feedback.

Nearly every source I've read says that replacing the Chinese rectifier tube is a great place to start if you want to get better sound out of the unit.

I'm just having a bit of trouble finding reliable, definitive information regarding which tubes to replace the stock ones with? I understand that the best tube is up to my subjective ear, but I'm just confused as to, technically, what rectifier tubes can go into the SL-2000a? (5Y3, 5V4, GZ34, GZ30, ect.)

I've read that going with a 5Y3 is a smart choice since "higher voltage = tighter sound." Any feedback would be appreciated or if anyone could point me to a technical document/white paper explaining rectifier tubes and their naming, that would also be appreciated. Personal recomdations as to what tubes and where to purchace them would be wonderful!

Thanks in advance for taking a minute.