I’ve recently used Audioquest splitters on a Benz Lukasheck PP-1 phono stage to add loading resistor plugs (otherwise its loading is fixed at 22K). This is not in my "best" system, but still very good. In fact I currently have a $4K WEL Signature LP cable hooked into these spitters (lol). I notice NO loss of sound quality from the splitters.
However, physical contact connections in the audio chain can be very tricky. If you have a single bad contact, it can very easily cause problems like (say) L/R channel imbalances. I’ve had headshells that have driven me literally CRAZY with this (answer: remove any rubber damping ring on the bayonet mount so the lead pins make better contact, then always tighten FULLY). Your need to periodically check and cleaning all contact connections. If and when you notice a channel imbalance, you need to go looking.
The Audioquest RCA splitters make a "death" grip on jack and plugs. The fit is VERY tight. Abnormally tight. Normally this ensures a good contact connection BUT if your equipment has those cheap PCB-mounted RCA jacks, it’s possible this tight action could crack and compromise things! Even chassis-mounted RCA jacks can become loose over time.