Short answer #1: Try it for yourself (it's your rig, room, ears)
Short answer #2: It depends
Long answer (to explain short answer #2): Purists would hate to not use direct connections to your mains (tops), but that would run them full range. Running through the sub turns the sub/mains into a sort of 3-way speaker. It will relieve the mains woofers from the bass duties (that take more power, adds intermodulation distortion, and prevents those woofers from handling more power and sounding more open).
While you're at it, you could also try varying the crossover frequency. 80Hz is the THX movie standard, but there is no audio standard. Lower crossover makes the woofers in your mains work harder, but could improve imaging. Results vary, depending again on your rig, room, and ears. Most audiophiles run their subs between 50 and 120 (for tiny mains) Hz. Above 200 Hz imaging would definitely be affected.