703 isn't some magic acoustic treatment... its stiff, which is nice when you're putting it on a wall... but seeing as you're talking about putting it between the joists, I'd recommend you get big old rolls of the like 10" thick stuff and plan on cloth coating the top of the room. The problem with 703 is that its only absorbtive to about 1kHz, maybe a little lower... which means that you'll still get the bounce in the lower mids. With thicker insulation in the ceiling you'll have a chance of stopping some of the lower frequency energy... the floor of the room upstairs will stay pretty transparent to most of the energy from like 100Hz and below so its really the lower mids you're worrying about [the classic problem with ceilings that are too low... you end up with a boxy sounding room unless you pay very careful attention to figuring out how to manage the low mid frequencies]. If you can "decouple" the speakers from the physical room you might have a chance of staying married a little longer... and if the opportunity presents itself, you may very well want to think about "floating" the room above your room as there won't really be a way to add any mass to your room, but if you add mass above your room and decouple the floor of the upstairs room from your secret basement hideaway she may be a bit less prone to stabbing you in your sleep. Best of luck with it!!