Speaker sound is probably the most subjective ideal in the audiophile realm. If you like Mission 770s and the JBLs, then you seem to enjoy a deeper sound with a bass bias.
My advise is to listen to a "brighter" speaker (B & W 603 s2 Anniversaries come to mind) and match them with a subwoofer that can be adjusted to fit your preferred sound signature for a 400 square foot room. A REL T/9x would give you the deep bass you crave while having the B & W's with their decoupled (37htz) tweeter and continuum mid-range provide a full spectrum sound. This set up with proper cables and wiring would be about $3,400.00. The B & W's also require solid power so that might require more investment. I realize that may be beyond the budget of the OP, but a room that size, can easily cost $10,000 to fill it with proper sound. Test listen as many speakers as you can with and without a subwoofer accompaniment to hone in your preferred sound signature. Good luck.
My advise is to listen to a "brighter" speaker (B & W 603 s2 Anniversaries come to mind) and match them with a subwoofer that can be adjusted to fit your preferred sound signature for a 400 square foot room. A REL T/9x would give you the deep bass you crave while having the B & W's with their decoupled (37htz) tweeter and continuum mid-range provide a full spectrum sound. This set up with proper cables and wiring would be about $3,400.00. The B & W's also require solid power so that might require more investment. I realize that may be beyond the budget of the OP, but a room that size, can easily cost $10,000 to fill it with proper sound. Test listen as many speakers as you can with and without a subwoofer accompaniment to hone in your preferred sound signature. Good luck.