If your problem is not the band in USA (Ainol AX1 works with 2G: GSM 850/900/1800/1900MHz and 3G: WCDMA 850/2100MHz) and you get "Invalid IMEI" try this:
1. You need a couple of old useless but clean (not blocked by IMEI, not stolen) GSM cell pho...
When I try flash v6.3 in SGS4 i9500 with TWRP "No md5 file found. E:Zip file is corrupt!" and instalation is "Failed". I downloaded zip file from different servers, different TWRP versions, and same result. Any idea? Any ZIP file to flash with CW