I should qualify my answer by saying I have only ever used a Paca and not a Capybara.
According to the SymbolicSound spec page on the Capybara:
"Is it possible to connect a microphone to the Capybara without first going through a pre-amp?
The Capy expects a line-level input so you have to pre-amplify a mic signal before feeding it to a Capybara input."
I think the audio input on the back of the Capybara are balanced which is why they are 3 pin connectors and look like mic inputs, but it seems they are not. You should be able to plug in line-level devices like synths and digital pianos.
In my experience, Kyma doesn't have racks of virtual versions of the standard effects in the way other DAWs do. So there aren't long lists of amplifier simulations (not that I've found anyway). If you were looking for that kind of thing then another DAW or effects processor might be easier. Having said that what Kyma does give you is very powerful basic building blocks that let you "do anything". So although it might be easier to use an off the shelf virtual effect, it can be much more fun and educational to build it yourself in Kyma. I've just spent a couple of days building a distortion pedal for my bass in Kyma. Yeah, it took me two days! But I've learnt heaps and come up with a sound unlike anything I've heard before.
The paca is different from the capybara. It doesn't have a built in audio interface, you have to get a separate one for it and plug them together (usually using firewire). I've got a Konnect24D and that does have both line-level inputs (for synths etc) as well as phantom powered mic inputs. It's got good gain control on it so it's quite happy me plugging a guitar in there too.