Some very nice small speakers are designed for bookshelves (Soliloquy, Linn, Kef all make some). You may do better with these. I would never use a rear ported speaker on a bookshelf. Front ports may work.
My biggest suggestion if you insist on keeping your speakers is a really nice small sub. This will greatly reduce the air movement and vibration from your speakers. If you can place the sub in the center (under the desk?), you could get away with a higher crossover frequency (200hz?). Otherwise, you can hide a sub almost anywhere, just don't cross it over above 120hz or so.
My biggest suggestion if you insist on keeping your speakers is a really nice small sub. This will greatly reduce the air movement and vibration from your speakers. If you can place the sub in the center (under the desk?), you could get away with a higher crossover frequency (200hz?). Otherwise, you can hide a sub almost anywhere, just don't cross it over above 120hz or so.