you can go to ntuc or any of those audio/diy shop in your neighbourhood, buy rca to 1/4inch(mono, with one black ring) adaptor and rca cables
or this(pic show a stereo phone plug, you need the mono one if you wanna get this kinda cable for geetar)
interconnect and you can use it(whether or not theres any problem with volume differences, its another thing thou)
Certain equipment come with the rca instead of phone jack cos its meant for line instrument instead of geetar/bass, when you mixed, it wont damaged anything, but there might be volume drop and impedance mismatch of some sort which dull the tone of geetar
Anyway, just trial and error
theres only 2 things can happen, either it works and discover some cool way of making sound or it didnt work.