Guitar + PC, one headset, help?

So what I have is 2 bass guitars, I have them being fed into a Eden bass amp (it only allows for a single input & output)

now this playing over speaker, and comp playing over speakers worked great when I lived with my parents

how-ever I have now moved out, so now my problem is, I can't play the bass loud (as loud as I would like at least) so what I want to do is have the music from computer & the sound from the guitar amp go to a SINGLE set of headphones

I don't want to pour a tonn of music into this, so a 'pro mixamp' like device is out of the plan

I have already tried to go from amp to pc's mic-in how-ever the quality sucks, there is alot of static feedback.

I do live near Manitoba, Canada so before you recommend products make sure I can get them in my area please ;)