I have a dedicated HT room in the basement with the following dimensions: (WxDxH) 4.38m x 5.48m x 2.35m

And I want to use 7pi´s as front, and make a center speaker with the same tweeter horn, and pi midhorn and a bassbox with the same woofer.

1) Would it be best to set up the front speakers on the short or the long wall ?

2)Would the 7pi´s overpower my room if I used them as rear speakers too?

3) Are the 7pi´s too forward sounding for rear speakers, would I be better off with a direct radiator speaker for this?

Placing the front speakers on the short wall will make the listening position in the middle of the room, and the rear speakers placed behind the listing position.
While placing them on the long wall, the couch would have to be up against the backwall and the rear´s too. Dont know how much this matters though.

Regards
Kim

The good thing about having speakers in corners is that you know the sound eminates from the corner apex and is limited to the 90º wall angle, consistently for each speaker. But with four speakers in a relatively small room, it might be good to shift the bass bins forward or inward a bit from the rear wall, to average the sound field and possibly fill in a null that might have otherwise formed. So take a minute to look at the references below, and you may want to spend some time and do an analysis of your room. That way you'll know if you want four identical seven π speakers in each corner, or if you'll want to move bass bin of the rear pair forward or something.

I suspected the short wall was the way to go for placing the front on. And I like to have the rear´s behind me instead of to the sides.

With analysis, do you mean calculating the room modes?

I have a Dlsa measuring system can I use that for anything room related?

regards
Kim

Check out Loudspeakers and Rooms, Part 3. It goes into the treatment of room modes in some detail. The Room Mode Calculator mentioned on page 11 is available here. The article called Loudspeakers and Rooms - Working Together is another good article. It has pretty much the same infromation, but it's presented a little bit differently.