Bookshelf speakers-double up,kef ls 50

Place them back to back and you'll get a bipole dispersion pattern. If you place them correctly you can achieve a very deep soundstage. A point source speaker like the KEF would be perfect for this type of experimentation.

Most amps will triple in power even! You could end up damaging your speakers or just playing way to much power thru them. 2 speakers connected to 1 AMP tap will make the amp see as much as 1-2 ohms! Most amps dont like this high resistance and will struggle or even shut down after a while.

Matt,
speakers in parallel will only load an amp. as long as amp has capabilities to drive them both per channel, one can easily experiment.
when CORRECT math is done, either 2 speakers connected to 1 amp or 1 will have same current going through them if amp doubles the power to the halved load or less current if the case is different.

I'm running an old Aragon 2004 amp and running two pair of Silverline Minuets in parallel hasn't presented a problem for the amp.

From the perspective of sound quality, I can only say that it doesn't sound as good as using just a single pair of speakers. It's hard to articulate. The sound stage was still there, but it got less focused. Blurry, if that makes sense. I ran them with the top pair inverted.

I also ran them using only the mid bass driver on the top pair. I got a good bit of the focus back doing this, but still feel that a single pair sounded better.

I only tried it because I happened to have the speakers. I really don't think that buying another pair of speakers for this purpose would be a smart move.

As a practical matter, stacking two pairs of speakers essentially doubles the size of your speakers. If you have the room, perhaps just getting a larger pair of speakers would be the way to go.