Hi Jacobo2u,
on bookshelves with little room between and behind says no rear firing ports. Form follows function.
My my first thought when you mentioned not being able to hear above 13khz is vintage. There are quite a few excellent vintage speakers that roll of around 13 to 16khz. And they sound amazing.
Something like a Goodmans maxim. The jbl D123 in a small enclosure would be nice as well.
I had an original ps audio sprout. A couple of times really. It's very convenient and sound quality was good. I trust Paul McGowan and PS Audio so assume that the Sprout 100 will be even better. Another option in the PS Audio lineup is the trio line of downsized separate components. There are even some out there with Cullen Mod/Upgrades.
if your looking for a nice all in one, had a Naim UnitiQute2 recently. Excellent piece of equipment. Don't let the low wpc output fool you. It's high current output can push some air around.
Ive also been want to get my hands on a Cambridge Audio Minx Xi