What do you expect a reviewers system to be

The only thing I "expect" is that it is a well matched system. If the system has components that are not known to work together well than I do not trust the reviewers ability to subjectively review a product.

I have no expectations for a reviewers system whatsoever, just as I have no expectations for any persons system. Whatever floats your boat.

What I want from a reviewer is a wide expeerience of various componennts. Both expensive and not so expensive.
To me the ideal reviewer would own at least two full two channel systems in different rooms. And have extra components in each available to compare.

that he or she knows the music being used well, and can explain to the reader WHY those music recordings display the items strengths and weakness, and what tho really mean in relation to other equipment choices.

And ifreviewers really did a good jobthey would compare the item to several others in that system. Swapping only the one item, for a variety of others and explain why the one under review was better or worse and why.

I'll expand a bit on your question to talk not only about their systems but also their credentials.

I expect what nobody seems to do:

1. Maintain an inventory of a good solid state amp and a good tube amp of 100 watts or more to give every speaker a good chance (many speakers prefer one over the other), and to let us know how it works with our preferred amp type.

2. Have their own 2 reference speakers so that they catch themselves from falling into love with one particular stylized sound.

3. Check their reference speakers against headphones too, for a third baseline that is also portable and room independent.

4. Listen with their ears and not try to play engineer/designer/physicist (unless they are one) to figure out what it might sound like or why it sounds the way it does - this only gives them prejudice which is almost always unfounded.

5. Not review equipment that is way more expensive than their own product of that type. They need a reference in the same ballpark, and to have experience with others in the same ballpark, as what they are reviewing.

The above would be for starters. There are many other issues of experience, honesty, lack of deep friendships with particular companies, favoritism due to advertisers, familiarity with real music (they all claim it but most don't go to many concerts, many don't go at all), and other things I could list, but we are not going to get even what I list above. Unfortunately, this is a cottage industry at the high end, and the reviewers are just as home brew as most of the designs, with little accountability (actually, none).