rega osiris vs simaudio600i or?

What's "better" is a value judgement...we all know that. It's like asking "how long is a piec of string?" ANSWER: "it depends..."

Simply put, I bought REGA R9 speakers to replace my TOTEM FORESTS with my existing bia-mped kit.
Then I heard the TEGA ISIS Valve cdp and REGA OSIRIS integrated amp.... blew me away!! Had to have them!!~ so I bought them both...money well spent!

So I sold off ALL my prior electronics and now have an all REGA simple kit: R9s driven by the OSIRIS amp and the source is the ISIS valve cdp.

IMO, it smokes the competition .... but just my opinion (key point: there is great magic that REGA synergy brings)

Give it an audition, you won't be disappointed.

I am using the Dynaudio Special Twenty Five and the Osiris drives them easily.

I have one for sale .. but in the UK

The Osiris plays way above its price point.
It soars even higher when partnered with the right source kit .... Like the Isis valve cdp .
Hooked me to the point that I scrapped my entire biamped kit and Totem Forests and bought them both.
Only an audition will tell but you won't be disappointed IMO.