Sony receivers typically can use two different sets of IR signals, which Sony refers to as AV1 and AV2.  Universals almost always provide AV1 signals,. but the STR-DG910 comes from the factory set to AV2.  You can change the mode.

The RCA RCRP05B (<$20) will work (on AV1) using setup ocdes Audio 1622 or 1822.   Or you could get a new Comcast DVR remote on eBay for usually $6 shipped.  Use setup code 30158.  Of course, the Sony RM-VLZ620 will work.  But in all cases use the instructions in the above link to switch to AV1.