Tube recommendations for AES AE-3 Preamp

Does anyone have tube suggestions for this Audio Electronic Supply pre-amp? I'm new to tube components, and I realize the perfect tube is always going to be a personal preference. With that said, I know upgrading to a NOS tube will be an improvement to reduce microphonics, and help combat the thin sounding digital music.

I have a tight budget, so any suggestions for 6SN7 tubes on the AE-3 would be great!

Thanks!