The first thing to upgrade would be the feedneck. Then, I would probably take care of the ASA. After that, it is all really just personal preference. Here is a list upgrades.
- Feedneck (CP makes nice ones, but you have tons of options)
- ASA (Again, CP makes great ones, but you have many choices)
- TechT Hush Bolt (Some people have good luck with this and others don't)
- Barrel/Barrel Kit (with it being an autococker marker, you can spend $150 on a barrel kit and it will most likely work on your next marker)
- Regulator (you could put a new reg on there if you want to, but the Azodin regs are actually pretty good)
- Azodin ZeRo Kit (it comes stock on the Zenith, but you can put it on the Blitz)
- Spyder Board (you could pick up something like a Spyder Virtue and it would work in the Blitz, you just couldn't use the Azodin eyes and Spyder eyes don't fit in Azodins. You would have a blind gun if you did this)