I've tried multiple cables.

I've even tried the unit at the store, to make sure that this problem wasn't exclusive to mine...

But I can't get a clear, clean sound when I run my PSR 540 into my digital recorder (Boss BR-8).

I've tried all kinds of things from RCA cables, noise gates, turning the volume on the PSR up, down, etc...

It's funny... I have a Zoom 123 drum machine that delivers crystal clear realistic drum sounds... and this is only a $140 product.

What do I need to do to get a clean sound (no hiss or noise) out of my Yamaha?