the best way to check ur phase is use test tone software, such as SinGen 1.2 (freeware)
start with 0 phase, low volume. set maximum hz crossover at sub, LF++ at speaker (in order to maximize the effect of overlap)
play a tone about 90-120hz which makes both speaker & sub exercise.
u listen closely to speaker, then switch 180 phase to check any cancelled out tone.
u can also check room mode reverb (usually 60-90hz) to reduce boom2 sound outside of room
in my opinion, sub (seal or port) should be located near 1 wall to get efficiency & great low frequency effects

u dont have to turn volume up causing it leaks outside room.
recommend 2 adjecent wall (like corner) for little sub below 8" only
some says down firing sub is easiest to get good sound

hoping hivi can make 1
Downfiring subs have a tendency of lifting the sub when bass note hits unless it was built extremely heavy. Don't think HiVi has any intention of offering them.