a Creative Sound blaster X-FI or even an older Audigy 2 may be useful to you, especially if you have on-board only sound.
The only problem with these, are the fact that Creative make these sound cards more suited to games, etc, so aren't capable of fully professional recording from outside without other equipment.
There are sound cards though meant for professional sound production, which will have all the inputs you'll need.
A Creative Sound blaster though usually comes with a dedicated front board, which you can plug a lot of devices into though, and one may very well be one of the guitar amp leads.
I'm pretty sure that these will be suited to what you want, as it is definitely a new sound board you need to produce better sound