I think I read somewhere that most of them are there but there is a subset that are not included with what is downloaded in the zip
Exactly. The Axe-FX II firmware provides these 28 XL cabs as syx-files:
1x12 AC-20 DLX M160 Off-Axis.syx
1x12 Roamer R121 Reverse.syx
1x12 TweedVerb R121.syx
1x8 EC Champlifier E350 #2.syx
1x8 EC Champlifier I5.syx
2x12 Class-A Tom's Mix Right.syx
2x12 Double Verb M160.syx
4x12 Cali M160.syx
OH_112_DLX_ALN-SLV_Studio-Modern.syx
OH_112_DLX_FN-42_Studio-Modern.syx
OH_112_DLX_J12-PR_SP.syx
OH_212_BOG-SH_FN-42_Studio-Modern.syx
OH_412_MAR-CB_EV-S_Studio-Modern.syx
OH_412_MAR-CB_FN-42_Studio-Vintage.syx
OH_412_MAR-CB_H-PR-55_Studio-Modern.syx
OH_412_MAR-CB_L-BB_RBN-121.syx
OH_412_MAR-CB_M-SB-75_Studio-Modern.syx
OH_412_MAR-CB_V30-CH_Studio-Modern.syx
TAF_ACRox_MIX.syx
TAF_Art+TangoJR-MIX.syx
TAF_Fen_MIX_ROOM.syx
TAF_Mars1x12_MIX.syx
TAF_Mars4x12_MIX_ROOM.syx
TAF_MarsBW_MIX_ROOM.syx
TAF_Shadow_MIX.syx
TAF_StarFound_MIX_ROOM.syx
TAF_VinMars+BWmars+ROOM-MIX.syx
TAF_WAT_MIX.syx