Preference for separate phono stages?

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

To contribute some more to this topic:

The best people to ask are designers of full function preamps on why they choose a single box solution. Talking to Allen Wright, he thought the main advantage was that one could avoid one more gain/buffer stage and the interconnect when combining pre and phono. According to Allen the problem with separate phono stage solutions is that they should be able to work with a variety of different preamps, requiring different driving and impedance-matching capabilities.

Finally from a noise perspective, I don't quite see the advantage of a separate case. One could always separate out the phono stage in a different shielded section of the preamp and keep paths to a minimum. The only thing that may be worth putting outboard seems to be the power supply IMO. I don't think that putting everything into separate cases is ideal, simplicity and shorter signal paths can have their own advantages, thus a single box solution doesn't necessarily mean a compromise.

Of course, the biggest advantage in separate phono stages IMO is the flexibility. Not only do you have more flexibility in matching pre and phono separately, but most external phono stages have more loading options too.