Your existing antennas and switch box will work for digital tv (assuming they are functional at all). What you need is a digital tuner for your old CRT tvs, which can only handle analog signals. The digital converter boxes will do that, but that box becomes your tv tuner, i.e. the means of selecting the channel.
However, you might benefit from an improved antenna as well. Quite a few stations changed their broadcast frequency when they went digital and some of them moved from the VHF to the UHF band. Older antennas were probably optimized for VHF, but those designed for the post-digital era will handle both bands. If tv is important to you and reception is poor in some places or some channels, you may want to invest in a newer antenna. One excellent one is the HD360 Mini-state. See http://www.amazon.com/Antennacraft-HDVIEW360-Mini-State-Antenna-Direction/dp/B001JT0FWY