Ken,
Unforutunately the only receiver that Dish has right now that sounds like what you want to do is the 721. The 501 has 1 tuner, so it will never be able to record one show while watching another one live. To do that, you must have 2 tuners. Which the 721 has, and your UTV has. Running another line to a 501 will do you no good.
As for hooking a 501 up, all you would need to do is unscrew the cable from the 301 and screw it into the 501. That's all there is to it.
Of course, the other option is to keep the 301 where it is, and add a 501 to the system. This would give 2 tuners at the same location, and the pvr capability of the 501 as well. You'd have to run another line to the 501, though.
Unforutunately the only receiver that Dish has right now that sounds like what you want to do is the 721. The 501 has 1 tuner, so it will never be able to record one show while watching another one live. To do that, you must have 2 tuners. Which the 721 has, and your UTV has. Running another line to a 501 will do you no good.
As for hooking a 501 up, all you would need to do is unscrew the cable from the 301 and screw it into the 501. That's all there is to it.
Of course, the other option is to keep the 301 where it is, and add a 501 to the system. This would give 2 tuners at the same location, and the pvr capability of the 501 as well. You'd have to run another line to the 501, though.