Ultimately, for $600, the Rega IO is a very good amp when driving 8 ohm neutral/warm speakers. Good when powering 6 ohm. And questionably hot and Inapproriately responsive to power 4 ohm or less.
Use it for 8 ohm and 6 ohm, and you have a good amp.
Use it for 4 ohm, and it’s long term...