Preference for separate phono stages?

Old AR pre-amps with phono are amazing (ie 6C). However, that is from the true old vinyl days. In the 80's & 90's most phono stages were just an afterthought. The phono stage in a cambridge 640 phono is way better than the internal phono stage on a $3000 sunfire IV pre/pro/tuner.

I do own a Shindo Monbrison - yes. Yes, I know it is possible to make a really excellent one-box line/phono unit, and in a small package at that!

It is, as I said, 'theoretical'. There are too many variables to make apples-to-apples comparisons. (I suppose you could do that if you took the same line/phono design and implemented it both as two-box/two-power-supply and one-box designs.)

the internal phono stage on my entry level Mac 6300 integrated is as good as my Graham Slee Era Gold external.

What about the Aesthetix Janus? I hear good things about it but have no first hand experience. Anybody who does?

Life is full of compromises. Otherwise we all would have four chassis monoblock amps and four chassis line stages and phono stages. The only one who can answer this is you. Yes, isolation offers a better advantage. The questions are: How much better? Can you hear it? How much are you willing to spend for it?

Some will spend hundreds of thousands to get that last 0.5% of sonic purity. Others will spend much less to get most of the way there. As with all things in the audio world, the law of diminishing returns kicks in early and hard.

Cheers,
John