A lot of folks already consider the Heresy too large for a bookshelf, but back in the day the Heresy speakers started and when JBL had the L100 Century, they were still considered bookshelf speakers. My Heresy II speakers are on a cabinet on each side of my tv and sound great.Even the Heresy II guts in a larger cabinet (Tangent 400) is way better on the bass side, and for most, that is what is lacking.
For many, a small modification to the original Heresy crossover will smooth out the sound, and make it more aurally palatable, but not add any bass. However, smoothing out the response allows you to turn them up more without taking your head off, and will make you think you have more bass.
Oh... welcome to the forums.
Bruce
What is this small crossover modification that you speak of?