It sounds to me that you would be happy with the 605. Your response implies that you do not use repeating timers on the 505 - you select a single program from the guide and choose the auto tune option. As I read the responses, this works on the 605 (i.e. individual programs can be auto-tuned).
The other part of the responses is if you want repeating timers (daily, weekly, etc.) there is no auto tune function - only auto reminders. These put a reminder message on the screen, and you have to push the enter key to see the program.
Is this correct??