If you happen to have a combination of transport and an external DAC the digital cable (BNC or RCA) has also the most impact on sound. Would digital cable consider as IC too? 
Yup, digital is something of a subset of 'Interconnects'
Really, I've personally found the impact of digital cables (whether coax or toslink...or ever toggling between them) to be rather smaller in effect than 'analog' interconnects. But, it's (generally) sometimes more cost effective to toy with your digi cable as there is only one of them
I've actually found IC's to be the most impactful of the lot...I just haven't found one that is 100% agreeable (as I have with the Alpha-Core MI-2). Perhaps one does not exist and I will wander in the audio wasteland of cables for all eternity
For what it's worth, Brad's Revelation Audio Lab 'Paradise' IC's are about as close as
I have found to (
my idea of) 'perfection'. They're just good - I just try to close my eyes at their cost (very labor intensive process to make these)