amp/pre amp utilizing two integrateds

So before I try this connection, I'd like to get a little input on the do's and don'ts. I am considering using a Rega Elex R as a pre amp for my Mac MA6450. As simple as the connections look and sound, I obviously don't want to ruin anything, and I have not attempted this before.
Pre amp output from Rega, to Power Amp in , on the Mac. and then there's the INT/EXT switch on the mac?
What mishaps could arise from this connection? TIA
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I presume the EXT will separate the preamp section from the amp section in the Mac! Do you have the owners manual?
It does exactly that, but which setting do I use? Am I safe either way? I have the online manual, and it really doesn't say much about it, only the back panel diagram.
I'm guessing that you are correct, I hate to guess
I would think that you would want to use the EXT switch so the amp section of the Mac is like a separate power amp. Throw that switch and see if the controls on the Mac stop working. If they do then you can use the Rega as the preamp. What position is the switch in now, INT or EXT ??
I took a look at the specs and manuals of both components, and I don’t see any concerns that would arise doing what you propose.

However you should absolutely set the Ext/Int switch on the Mac to Ext when doing so. If you don’t, depending on how the design is implemented the result might be that the outputs of the preamp sections of the two components would be connected to each other. Which in turn would give very poor sonic results and would also stand a good chance of being unhealthy for one or both components eventually if not sooner.

-- Al