The Majik I integrated would act as a preamp only connected via its preouts with The Majik 2100 power.
Which version of the Majik I, and 2100?
If both have Dynamik, they are going to sound similar but the 2100 will improve the performance in terms of tune. Not a lot, but it will be there.
If neither do, then it's the same difference.
If Majik-I has Dynamik (must be a newer one then, the older ones don't support Dynamik) and the 2100 does not, don't bother with the 2100 unless you want to purchase a Dynamik for it.
If the 2100 has Dynamik and the Majik-I does not then it will be a pretty noticeable difference as zee points out. It may or may not be to your liking depending on the speakers, but personally I like the faster, cleaner, punchier sound of the newer Chakra amps. The older amps sound a bit slower and "rounded" in comparison. Musical to be certain either way.
I am not sure which speakers you own but assuming the Majik-I and 2100 have the same relative gain then you can consider bi-amping. You would need to determine which versions of the electronics you own to see if this is possible.