K series is going to sound a good deal better in smaller boxes, but albiet ported 12 v 12 the 3500 is going to take the cake in terms of sheer output. Just one peaky sub. Definatly a fun toy of mine at one piont in time, would also be a good candidate for IB use. K imo will retain a good better deal better response ported in smaller boxes and imo retains a tad more composure than the 3500.
K series will NOT handle the power a 3500 will, sheer spl wise, the 3500 takes the cake imo. 12 v 15. Never personally made the comparison but in terms of output it'd level the playing field a tad.
Ben