I'm finally getting rid of my lo-fi stuff after 30+ years and could use some opinions. My listening room is 12.5' x 13' x 8' with three walls covered with guitars and guitar amps and a small desk. I'm currently listening to some Polk Monitor 5B's I bought  nearly 40 years ago and just recently upgraded. They are about 40" from the front wall, 5.5' apart, and about 6' from the drivers to my listening position. I also have a pair of ART arrays that sit behind them.

I've been thinking about a set of small OB's and remembered the Caintucks.  I've heard plenty of OB's in the past, but not sure how well they would work in such a small room. Anyway, would the Fast-8 or the F15's be better? I could supplement the low end by building a couple of 8" subs which would be small and fairly unobtrusive.

I was also looking at the Manzanitas as I"ve heard them many times over the years, but he 12" is unobtanium in the US, and the 15" version is visually "in your face" because they are on stands. I mocked them up and if I have to listen to them in the nearfield it would be like a couple of walls right in front of you.  If they could be a couple inches narrower and go to the floor it wouldn't seem so obtrusive.

Any suggestions or opinions I'd most welcome.

I'd post a drawing of my room layout, but I'm new here.

I just now saw your post.

I have been using the Lii Audio F15 in a 36" tall, rounded open baffle for almost a year now. Basically, I scaled down Steve's bigger 42" baffles.
The Lii drivers were pretty stiff when I first got them and it took some time for them to loosen up a bit.
Now mine sound great.

I have a number of subwoofer systems on hand I can use. For some types of music an extra octave down low is called for. I listen to all kinds of music.

About 90% of the time I have a subwoofer system sitting there at the ready, but it is not active.
I mainly turn on the subwoofer system for playing classical or rock music, but I mostly play jazz and occasionally some soul, funk or Motown variant.

Depending upon your listening styles, you should be fine without a subwoofer for quite a while, once your F15s are broken in and sounding right. But, if you're a metal head, you'll want some help down low, right away.