Will one cable upgrade make a noticeable difference?

I think you have good chance to hear a significant difference since you would have more brand synergy. The question is would you like the difference in the sound. I always take the risk and try myself. We can resell if not as hoped.

@cantorgale 

HI Cantorgale

Only today I read this question of yours. Replacing cables can be a great upgrade. The secret is to always start from the power supply, which is of fundamental importance for all HiFi/HiEnd systems. So I did and I immediately heard a big difference with a much better sound. Then one cable at a time I replaced them all and now I enjoy the music as much as possible that my system can give. It is important that all cables are of the same brand and of the same series... the synergy between them is fundamental in my opinion.

For your information, my system is as follows:

Audio Analogue Puccini Anniversary Amplifier, SME Model 10 Turntable, SME Series IV Tonearm, Sonus Faber Olympics II Speaker, Benz Micro PP1-T9 Pre-Phono, Benz Micro LP Cartridge, Lyra Titan i Cartridge (with load adjustment through 100 Ohms Audio Note resistors), Streamer/DAC Homemade with IAN CANADA parts and all cables (power, speaker, interconnect and phono from Audio Analogue Airtech series ZERO (Top). Finally, consider that for my top listens, Vinyl remains the best.

Kind regards

Alessandro

I have transparent cables and also have the power isolator. I would call customer service in maine for insight.  I found them especially helpful. Also got power cables from them as well and interconnects.

Overall it makes me feel more comfortable with what I'm listening to and reduces the need to be critical.  If you have a great system it will help things a lot better. But it does bring out recording quality differences which is annoying in its own right. 

And the farmer hauled another load away !! 

Question: Would replacing the SR with either a Transparent G5 Reference or G6 Ultra make a noticeable difference in the sound?

Likely Yes, no guarantees.

Or other suggestions? 

You have a very well balanced system.  Upgrading PCs would likely be positively noticeable, but low of diminishing returns it may not be worth it.  Maybe try/borrow a higher quality PC to try on each component.  Otherwise, the change would have to be your choice - changing the speakers or electronics.  

Another option is to add vinyl.  I have both.