I agree with Jason above. Do whatever you can to avoid the HTIB route. Since you say the shelf is portable, I assume it is not built into your wall so I also wonder why you accepted it. Unless the instructions to the builder, regarding the 17.3" width, were not in writing. If not, unfortunately we all know the outcome - classic he said/she said argument.
I'm afraid the product you want that will meet all your needs as outlined in your OP, simply doesn't exist. So the way I see it, your stuck and something has to give....
1) You can either suck up the $350 spent for the shelf and start cutting it yourself to make the necessary modifications. 2) Or you can forego 3D and look at used Pioneers AVR'S (pre 2011) and hopefully the 16.54" will fit. 3) Or live with a HTIB.
Again, if it was me, the last one is unacceptable and I would make the hard decision between number 1 or 2. Sorry.
Marantz PM15S2 LE, Arcam FMJ CD-17, VPI Traveler V2 with an Ortofon Rondo Blue, Technics SL-1400 with an Audio Technica AT-14sa, Simaudio Moon 110LP, Pro-ject Phono Box S, Pioneer Elite VSX-52, Pioneer Elite BDP-52FD, Dynaudio Focus 260's, Vienna Acoustics Theatro Grand, Wharfedale Diamond 9.2s, REL T-1 & Panasonic TC-P54S1