How to level match when comparing components?

Then you have the real problem. Which do I *like* better, which *is* better

I hope you are joking. If those two are different in your mind, then you do have a real problem. If you start trying to please someone else, or second guess some "absolute" or objective then you will never be happy with what you choose. The only thing that should be of concern is what sounds best to you, assuming you are going to be paying for it and living with it and enjoying your music through it. I guess if you are buying as a gift for say, Micheal Fremmer, then you should probably be concerned with what he thinks....otherwise it's up to you.

Listening in your home listening room is the best way, and as already suggested, at least a week of each player is best. All else is guessing.

I diagree with ojgalli as to the reasoning.
He is doing an immediate and sudden comparison. relying on attempting to remember a snippet of sound. My (and others) rely on long passages, and NOT so much on memory of the actual sound, but on how the sound made you feel. That feeling is easy to remember. And if it is repeated, the collected feelings of each product with the different music can give one a clear preference, which will last when actually owning the product.
One will remember some of the highlights of the sound, but the meat of the comparison is the emotional response.

An additional thought:
we judge with the thinking side of our brain. We enjoy with the feeling side. (yes this is simplistic, but forgive me)
When we are auditioning, and just using the thinking side, we skip the part of our mind which will be the part that enjoys or dislikes the sound, in the long run.
So by including the feeling side in the process of auditioning, we can fufill the need of our whole mind.
The feeling side needs time to form it's 'opinions' the feelings. Then WITH the feelings included in our decision, we will be happier with our choices.

The OP asked a simple question. The answer pink noise and a db meter.
He/she is not asking whether one should be analytic or emotional regarding component comparisons or what the requisite period of time for a valid comparison.