I don't know how big that unit is, but if it's larger than a box of Tic-Tacs it will not fit in the dash behind the HU.
If you have some wiring on the Sirius unit to work with, you can remove the glove box and install it on the left hand side behind the center console. There's much more room there.
Pioneer head unit, PAC steering wheel control modual, Hard wired Sirius radio, Hard wired radar detector, Piezo beeper for locking doors, Tinted front side windows, , Mini Maglite holder, D-Cell Maglite holder, Weathertech Digifit Floor Mats
BHLM, T-Rex Eyelids, Air horns, Blacked out badges, Smoked Tails, Black Powder Coated Billet Grill, Hella Black Magic Driving Lights, Color Matched Engine Cover, Lund in channel vent visors, FJ Cruiser alloy wheels, Leer 100XQ shell, OEM bed mat, Black Westin bull bar, 4" black Aires tube steps
Bed lights, Guage cluster lights color change, Bilstein 5100's up front