I did the exact same move...S5e to S8e. The soundstage width just opened right up with the 8's...the 5's had to be cranked to rediculous levels for daily living to fill a room. My shock with the sub has been less about adding bass as opposed to reinforcing the mids and highs...I feel that the additional bass actually helps the full range. You are correct that a proper sub can be hard to find for a given speaker. My only regret with the Spendor Sub has been its true intent to go with the monitor prevents it from reaching 20Hz...therefore it blends well, but I am still missing some of the potential depth another brand would bring...it is also therefore not as good on movies as well (not a big air mover).
Happy listening
Chad

