I think it depends on the current state of your system. If you're already completely outfitted, I would say wherever your cabling is the most compromised, whether that be interconnect or speaker cables. If your speaker cables are overly restricting the music, then spending a lot on a digital IC might not yield the results you hope for, if any at all. In that case changing speaker cables could make the biggest difference.
If you have no cables at all, have a single matching brand throughout, or have different brands of cables but at a similar performance level throughout, then I would agree with what the previous posts mention about getting the best cable starting form the source first.
I'll add something that might confuse you even more. The biggest improvement I've ever gained by changing cables was with a power cord upgrade. Sorry. Good luck!
If you have no cables at all, have a single matching brand throughout, or have different brands of cables but at a similar performance level throughout, then I would agree with what the previous posts mention about getting the best cable starting form the source first.
I'll add something that might confuse you even more. The biggest improvement I've ever gained by changing cables was with a power cord upgrade. Sorry. Good luck!