How important is the amp?

Mordante,
this is probably a biased view since I'm a big fan of Symphonic Line amps myself. I've had experience with the RG4 Mk3, RG1 & Kraft 300 amps. Symphonic Line amps are really very good & can drive most speakers. So, if it were me, I'd wait till the last minute to upgrade the La Musica amp.
having Said that a friend's friend got the Kraftwerk & found it to be a superb amp. I don't have knowledge of how the La Musica & Kraftwerk amps compare.

If you like what you hear and can hear differences when you tweak then I can't think of a good reason to change.

Wait, oh yeah, because there is always something better!!! of course! You never know for sure sometimes unless you try.

If you are content, you will just enjoy listening to the music. If you are not, don't loose sleep. Look for something better now! Money and time is all you have to loose.

Seriously, only you know if you are happy with what you have, but in your case, it sounds like the vital signs are good.

The amp is very important.It was the combination of power, control and overall coherence that made audio system work well seemingly with all musical genres.

and amp to a stereo system is like an engine to a car

Mordante hi,
For what amp will sound the best for you really need to see an impedance/-phase angle graphs on them, I've looked for you and there's nothing.

Failing to get these graphs, the next best is to email the designer and ask them if they have the graphs or last option if they recommend what type amp drives them the best.
Before getting on the amp merry go round, to find what amp drives them the best yourself.

Cheers George