From your photo, I don't think you'll have any major problems. I have my SongTowers similarly arranged around a wider and deeper wall shelf system. My photo shows them moved in front of the shelves, but I think you can see what I mean.
http://api.photoshop.com/home_7e53687d13c747d28ccec9a6980c7256/adobe-px-assets/2b778c95c2ce45f6aa432373d67150a3
SongTower dimensions:
Overall height: 47.5" (including plinth & spikes)
Plinth: 10" wide × 15" deep
Tweeter height: 37"
Lower woofer height 29"
As long as your leather chair doesn't significantly block the lower woofer, it should not be a problem. I think the tweeter is high enough to be well above the chair's arm.
SongTowers can be placed back against the wall behind them (or as close as the plinths allow) without harming the bass sound. This goes against the conventional wisdom, but it has been confirmed by their designer and many owners, including myself. Because the midrange and higher frequencies have such wide dispersion, these speakers are not at all finicky about room location. You may find that you entire sofa will be within the "sweet spot" where stereo imaging is at its best.
As long as you place the front of the SongTowers so they are at least even with the front edge of your wall unit, you should be fine.
Congrats on your decision to get SongTowers! I am quite confident you'll love them. What finish are you thinking of. My photo shows unstained cherry.