You will be boring people with what a steal these guns are in no time.
You are going to need the reg'ed bottle - 1800 psi output gets the .22 up over 23 fpe - and an adapter to screw into the Hammerli/RWS valve. Bryan and Assoc. sells the adaptor, call them and tell them you are attaching a reg'ed bottle and need the adapter. You'll probably need a stronger hammer spring - the spring from the Hammerli Dominator is what most on the forum use - with that output pressure.
Here is a link to the DIY section of the Hammerli forum. Everything you want to know is here:
Mine is a 12 fpe .177, I haven't done the .22 conversion...........yet.