Differents between the synth roms

Hi,
I wondering what is the different between the synth rom to EIV classic and Ultra.
The upgrades to classic are 6320 and 6321. The ultras cit 6870 and 6871
Can I by e-synth cit to my e6400 classic?
I wondering what is the different between the synth rom to EIV classic and Ultra.
The upgrades to classic are 6320 and 6321. The ultras cit 6870 and 6871
Can I by e-synth cit to my e6400 classic?