I haven't really swapped mine much. I put some 70s gold pin Mullards in mine a few years ago and they stayed. They sounded much much better than the original Counterpoint tubes and the JJ/Tesla replacements I tried. I did notice slight improvements when I upgraded the Power supply tubes (more dynamic, better bass, etc), but the line stage is where you should focus most. Those Aperex tubes should be great if they're not too noisy (and you like the sound). You could try them in the power supply too, but that might be overkill.