RCA interconnect recommendation

@millercarbon is quite right. An expensive interconnect can have a component level effect on a system. I have had three systems around for a long time. Occasionally I’ll swap some rediculously expensive cable into one of my less expensive systems, it might have big improvement, none, or sound simply atrocious. But typically a component needs to be of a very high sound quality before real positive results are gained.

As you obviously realized you can put a lot of effort put into assembling a good system. If you are willing to work like a mad man, you can assemble a great system for less money... but it takes tremendous effort. MC has put in the effort. But it takes effort and time... years learning how to listen, understanding sound, components, interactions. It is pretty easy in the beginning to make mistakes and get yourself into a negative feedback loop.

Hence, some basic rules of thumb can help. Hence, the idea of 10 - 15% investment in interconnects. The idea is you need a bit of guidance at the beginning. Plunking down $5K for interconnects for a $5K component is not something guaranteed to be a good investment. On the other hand some of the really inexpensive cables recommended here are also no better than what is supplied by the manufacturer. Until you really know what you are doing it is probably going to be true that putting an extra $5K into a well chosen component (valued at $5K) is a better investment than using that $5K in a set of interconnects. Typically a well chosen $10K component will sound far superior (big difference) to a equivalent $5K component.

The best strategy is to invest in the very best possible, compatible components. Get to know them intimately, inside and out... while saving money (for the next phase of the process). Then look for and evaluate interconnects and cables... this is a very time consuming ( and fun... hopefully) process. Then tweak... isolation, power cords, etc. if you try to do too icy at once it becomes really confusing... especially if new to this. I have spent literally thousands of hours evaluation components, interconnects and tweaks over the last 50 years... so has MC.

I have also swapped an expensive cable into a system and literally have a jaw dropping, component level change in the sound... but that is not the most common change.

If you feel the need to buy expensive cables then do it but I would rather,use my money on something else.i don't feel you will hear a difference....but its only my opinion...

For the digital cable, try to get a true 75 ohm cable. Most are not, and frankly RCA plugs are not 75 ohm (its a stupid standard, get BNCs!, ok rant off)  It must be intended for digital or will distort the threshold crossings that determine timing.   fo he analog side, its....analog. So the same rules you apply to RIAA, preamp-power apply.

Yea, cables matter.  Unfortunately its often because engineering is ignored and not in a good way.

ghdprentice and miller carbon much appreciate your time and everyone else's who wrote their thoughts.
I think I'm a fair to good listener. It's a curious problem of "you don't know until you know" sort of thing. I hear immediate and subtle differences.
Where am I in this? Well I'm closing on a year in putting this system together and I could stop here. I'm pleased with it and I've learned an awful lot.
Yes I understand about making changes slowly in order to evaluate.
I'm very pleased with my TT, cart and phono stage. Hope to have them here for a long time. Maybe I'll try rolling some tubes in the EAR but I don't have a reason at the moment. Maybe a Boston acoustics carbon mat? this is likely.
If I had to guess the future, I could see a different amp arrangement in the future and also speakers but I'm not there yet.

Does anyone have experience with the cable company lending library? And is it worth a try?

Study what ghdprentice says above. There are many, many things that make a great deal of difference that don't cost a lot of money. Some of them do however cost a lot in terms of time and effort. To give just one example, things like springs might not seem worth doing. They totally are.

What happens is they force you to listen close and evaluate. You can do this with a cable, speaker or amp too. But with those it is very expensive to change. With springs it is easy, simply change or move the spring. Total cost: zero. Same with things like routing cables. Another novice tried that and was shocked to hear a real significant improvement, just from moving wires around.

Every time you try something like this you learn a little bit more. Not only about what does what, but in terms of how to describe and evaluate what you're hearing.

Then when you go to buy say an interconnect you're not all, "What can I spend for $500 to go between this and that" but instead are, "I'm looking for great depth and layering, not up front in your face detail, who makes a cable like that?"

See the difference?