Why not put the EH tubes back in and see which ones you like? The Amprex should have plenty of life in them if you use your unit normally. I have a Ah! cd player with the Amperex tubes and after 6+ years they are still great.
Tubes for Eastern Electric CD
I bought my unit 4.5 years ago, changed from the EH6922s to 2 Amperex 7308 USNs. After 4 yours I am not sure if they are degrading as i do not have a tester. Wondering what other tubes people have found to be a good match. I have TAD 150 sig pre TAD 125 amp and Vandy 3a sigs...