Unless you can DIY, those solutions are a terrible idea.
The center speaker in that resonant space will have very poor speech clarity.
The big problem is that speakers are designed to be in free space. There is a drop off in response when the speaker transitions from half space to full space radiator. When the speaker is not in free space it is over corrected. This is called baffle step compensation.
So if you are going to do that, then you really need to be able to design and build your speaker and voice it the space and location.
I do have a small system downstairs that is a cabinet type situation.
Notice there is no center channel. The left and right speakers fill almost the entire space in which they reside. There are books to the inside of each speaker. The case is set into the wall under a stair case. I designed and built the speakers and voice them to space and location.
The usual outcome of these type of situations is not good.
The sub is the least of your problems.
My subs are not in the cabinet.
Even though this is a very pleasant system, I would only do this for a secondary system.
You are much better off just having the electronics in a cabinet with enough ventilation, and having good looking free standing speakers.
And that is another issue, cabinets can be real destroyers of electronics due to inadequate ventilation.