I have been looking and found a number of speaker switchers that allow for the trend of dual or more centers and still keep an 8ohm load. Here is a link to one.
speaker switcher

Actually, from their documentation, it is safe to infer that 2 8 Ohms will be seen as 4 Ohms. Their special circuits are triggered to maintain 4 Ohms, which is why they need an amp that works fine at 4. This is good news for VP-150 in that 2 6 Ohms will be seen as 4 Ohms instead of 3 Ohms.

I wonder what its transient response is like.

I saw a number of them today, I know one said it would maintain 8ohms, obviously not the one I linked to, but you get the idea.

I wonder what FREQUENCY response is like ?

The box itself is flat 20-20K, which makes sense, but unless it has a built in power amp it must either wire speakers in series or insert series resistance to maintain an acceptable impedence, and both of those are going to have some impact on frequency response as the speaker impedence varies with frequency.

If it's just wiring in series-parallel that wouldn't be too bad, but series resistance would have a pretty big effect on the frequency response of the switcher/speaker combo.

Or use transformers. Which is why I was asking about transient response.

Interesting idea. A transformer fits the "impedence magnifying circuitry" description better than series resistors or series-parallel switching.