Impedance match


My understanding for impedance matching a preamp or upstream source having a volume control (e.g., a DAC with volume control) to a downstream amplifier is that an appropriate “impedance match” is for the amplifier to have an input impedance at least 20-fold to 50-fold greater that the output impedance of the upstream preamp or source output impedance. One dealer told me that the appropriate “impedance match” between to such components is exactly that—an identical match of the same impedances. 

So which is it?
128x128celander
None of this makes it easy for us non pro-audio educated to make a correct purchase of a pre or amp/s
Tweak1, if one picks a sufficiently high impedance ratio, say 20-fold to 50-fold (or more), then one might cover all of the frequencies where the low impedance ratio is avoided. 
What I mean is (and I do not consider myself a typical component purchaser is: this topic has never been explained or mentioned in any component manuals

I have probably flipped through 10 preamps/amps in the last 15 years

I can't help but wonder how much it had to  d with impedance mismatches 
I think the concerns around "impedance mismatch" are somewhat exaggerated for most "typical component purchasers". By far, most of these purchasers either buy an integrated amplifier/receiver or solid state separates where the (separate) preamp almost always has an extremely low output impedance. Tube electronics, particularly separate tube preamps could pose some matching concern but those are usually purchased by more demanding, and sometimes more knowledgable  customers.