A little more detailed info is needed. First of all, if you bought a digital converter box like the ones that were sold during the digital transition (Insignia is one brand), those will pick up the digital signal but that's all. They are not HDTV converter boxes. I have a couple of those (back bedroom analog tv, garage analog tv) and all they have are RCA outputs (red, white, yellow cables). Quality will be ok on a small crt tv but a new LCD, probably not. Second, there is really no such thing as an HDTV antenna. You just need a good antenna that can pick up UHF-VHF signals depending on your area.
The digital tuner should be connected directly to the tv if the tv is HD-ready (no built-in ATSC tuner). Running a digital signal only to the AVR will not convert it to HD.