There is a way around it, although I do highly recommend you think about some things before purchase...
Nevertheless, when you are assembling it, before you drop the glass on top, you drop the speaker in. That will do the trick. However, if the speaker really was too big to "slide in", that obviously means you have to remove tv, and glass to get the speaker out. Not too big of a deal probably.
I have 2x
Studio Tech modular racks, at $200 a piece, also from racks n stands. I split em sorta, and have one bigger one and one smaller one. You can buy extra 7" or 9" posts. Great value IMO. Only downside is that to reconfigure for more, or less, racks, you need to take everything out and turn the rack upside down.
The benefits are future proofing for more or less components in the future. Better ventilation. You will not have ambient light directly below the tv, which can only improve contrast/PQ/immersion. You will have a much less chance of terrible center speaker positioning/setup, without glass reflections from both above and below speaker. You could hope to acheive better dispersion with more accurate response.
A few things to consider. Now that I have a rack to the side, I don't think I'll ever do a conventional TV stand again. Could be famous last words, but that's my prediction.
-jostenmeat