I think only WCET-DT currently(according to the info from my audio receiver/decoder anyhow), is capable of DD 5.1. The rest are just DD 2.0/Prologic.
Speaking of WCET-DT, they appear to be off the air currently, or at very, very low power. Noticed the audio was missing most of the day too.
Concerning your reception, It's really hard to say how your digital reception will work out with an indoor antenna, if you're seeing the analogs well(no noise or ghosting -- Especially so if you're getting good, or at least decent quality reception from say, 19,25,38,48 analogs) with your current antenna, I'd say, currently, you at least have a shot of getting reception of some sort from the Cincy ABC, NBC, CBS and Fox digitals. However, since you're about 20 Miles out, your best bet would be a directional antenna mounted outdoors, such as a small-medium VHF/UHF Combo(Yagi) -- (Cincy ABC is on channel 10 VHF, BTW). This, with a rotor, or 2 antennas on seperate feedlines would give you a good shot at the Dayton stations as well.
Not sure what antenna you're currently using, but, a better antenna indoors might help for Cincy stations too, near a window that faces the transmitting towers is probably the best place for an indoor antenna. Besides Yagis, Bowtie type antennas can work well on UHF, "rabbit ears" might do it for you on VHF for channel 10, given the antenna is placed in a nice "sweet spot", which you may be able to find via experimentation.
PBS Cincy(WCET-DT w/PBS HD), and (WSTR-DT(WB - No HD) are currently running at low power and would most likely be difficult from your location with any indoor antenna. WSTR-DT probably moreso because their directional antenna doesn't send much energy your way. WCVN-DT (PBS/KET - No HD yet, 4 channel SD multicast) in N KY would probably also be difficult from your location from indoors.
In any event, if you want, nothing wrong with trying your current antenna out when you get your STB ... See what you get before "moving up", if necessary or desired. Just a guess, but, if you can find a "sweet spot" to put your current antenna, I'd guess you'll get something, at least from the high power Cincy DTV stations.
Good luck and hope this helps,
update: DT_parker -- Sorry for pretty much repeating the same info you provided, that's what happens when I type while watching HD "Alias" <g>