Airport Express & Another Router

Hi.

I currently have my airport express connected to my wireless router so I can browse the internet and stream music at the same time. My airport express is downstairs with the sound system, and my wireless router is upstairs, which can't be moved. The problem i'm having is that the music in itunes 'stutters' because the airport has to reach upstairs to connect with my wireless router and come back down again. Does anyone have any solutions? I will be very grateful if you do.

Thanks, Thomas