On the Rolandclan forum you can read a lot about it if you see through the first threads from the time when the FA came out. Many users had a wrong idea about the Axial sound packages. The only ones that really contain new sounds (new waveforms) are the EXPs to be loaded into the 2 slots, and these are 1:1 the old SRX expansions, you can compare the respective PDF sound lists. (One or two EXPs, e.g. Ultimate Keys, even lack a few waveforms from the SRX boards).
The other Axial packages are SN-Synth sounds, but not with new waveforms, but just sounds programmed out of the existing SN-Synth waveforms in the FA.
I love some of the SRX expansions especially for their orchestral sounds, but they are not very strong regarding acoustic solo sounds like saxophone and trumpet. And the 2 slot restriction is significant to me.