AWenta, are you asking me? I'm not using any subs as my full-range speakers go down to about 20Hz (on a good day). So staying with my philosophy of less is more, I have less yet.
If you're into the quality of sound at all, let's say the "believability" of the playback presentation, I'd advise not going the in-wall route. Because we're talking playback with 2-channels/speakers/sound sources rather than a live band, the speakers need room to breath. Hence, placement within the room is critical and to get any kind of resemblance of a 3-D soundstage (which adds much to the believability), the speakers really need to be a minimum of about 5 ft out from the back wall. Mine are about 7ft out from the front speaker face. Soundstages are generally deep and wide. But if you paste them against or make them flush with the back wall, the depth is gone as is much of the width. Your approach may look aesthetically cleaner, but it won't get you any closer to a live music presentation. In fact, it will take you in the opposite direction. But of course it depends on your goals.
BTW, any bass from these in-walls will suffer greatly. Speaker placement within the room is most critical for bass notes. Poor speaker placement and your bass will be the most ill-defined, wooly, boomy, and rolling earthquake-like bass. Like you might hear in gansta' cars. There's nothing real about that, except that you feel like you're getting an enema and you didn't even ask for one. Superior speaker placement offers you the best opportunity at generating the tightest, deepest, most well defined, musically accurate bass you've ever heard. If you ever heard the 2 side by side, there's no comparison.