Hi DB, thanks for the kind words.
I think that the speaker cutout that you see is for the bass sub-woofer (which is rear facing) and this, in turn, has a downward facing port. There are also a pair of 50mm (downward facing) middle speakers and another pair of 50mm left and right facing stereo speakers. These are driven by a small internal (low power) amplifier but there will be a take off for an external amplifier (if required). There is a panel which fits over all the individual, internal speaker enclosures and those enclosures (except the woofer) should be reasonably air-tight on the inside.
If it all works as intended I shall be well pleased (and possibly amazed) but there are no guaranties as this is all being done off the top of my head. There are no actual drawings or plans and it is just taking shape as I go.
Tweakie.