Hi Fi Choice (UK) featured a six integrated amp shoot out and the Rega Elex R won. The Naim Nait 5si finished second. The speakers used in the test were ATC SCM40 wired with Nordost Frey cables. All amps used Valhalla 2 power cables with a Nordost power conditioner. Sources were Cyrus cd transport feeding a Chord Hugo dac and a Project Expression table. With this equipment the amps were allowed to perform at their best. The Rega was also less expensive than the Naim. The report ended with the Rega being the most musical and engaging of the amps under test. As always personal preference will make a difference. This was also reported as a blind test.
I have no personal experience with any of the amps.