Get a used 500 series. That should have digital out. Why mod a cheapo unit? Upgrading should cost less than having your unit modified. It may pay to ask dishnetwork what it will cost to upgrade. You can always cancel and then sign up again under someone else's name in the house.
The digital out would still be stereo only on the 301, while the better receivers will allow Dolby Digital. I also love have a hard drive in the receiver. It is quirky but awesome-scrap that vcr.