Speaker/Equipment Placement

"From an audiophile perspective, is it preferrable to have nothing in-between the speakers?"

Definely preferrable, as it add depth to the soundstage.

It is preferable but it is not a disaster if you do have something in between so long as it is not too tall and too close to the speaker to cause major reflection.

I tried a bunch of different setups after moving into new digs two years ago -- equipment in between, equipment rack off to the side, moving everything to another wall and then trying both again. You get the idea. I always ended up enjoying the music most with the rack somewhere other than between the loudspeakers. This may vary if you can get the speakers well off the wall, but as I'm limited to two to three feet, it always made a difference to get the space between them clear of stuff. This has been true, by the way, with four different pairs of speakers and with a few different electronic setups.

Keeping everything away from the speakers is the best approach, but reality says otherwise! Isolating the components is good, but don't put them in a location where standing waves form such as a corner. If the components have to go between the speakers try to keep them as far behind the front plane of the speakers as possible. Most box speaker only radiate the midrange on up (which you are most concerned with for this discussion) from the front so things behind the front plane have minimal effect. Dipoles or omnis are another story and keeping the equipment away is the best thing for them.