hd15s + cubo 15s?

anybody's opinion? Never heard a similiar combination so not sure whats best

Not sure 1 hd 15 per side would add much kick, as these are best in multiples. Plus you will need additional amps / crossovers with appropriate delays. May be better with 4 cubo's and build a mid top to get down to 120. x12 or 15 maybe.

Going 3 way would normally add extra oomph to a system over 2 way, depending on the speakers involved.  Something like HDs would cover the range between the subs and tops, so the tops and subs could be crossed over lower and higher respectively.  With less bandwidth going into the amps/speakers you can utilise the power you have and turn things up some more!

If your tops or new mids can cross low enough to meet the 4 cubos and play loud enough to keep up with them that sounds like your best bet, especially given the music choice...

Have been running exactly that setup last 2 years:

8x cubo's with 4x hd15's with  mid/high.

in my case the mid/high was 4512's with 2" above wich has been replaced now with 2x MT121

The 4512's where to much of narrow mid cannons and you would miss the mid in front of the speakers, so i suggest you take a wide mouth mid horn or even plain reflex mid to make sure you get the front filled with mid too.

For the rest it was bomb, hd15's really boost the cubo experience, my cross settings where after some experience: cubo's 40 to 95 and the Hd15's 90 to 160hz then the mid would take it over. no gaps ;)

greetings, bart.