There are a lot of possible RCA TV codes programmed into the DTA800B1 remote.
Try the following three digit codes: RCA 000, 001, 005, 072, 073, 074, 075, 076, 077, 078, 135,
138, 140, 144, 150, 156, 159, 162, 163, 169, 171, 178, 229, 246, 249, 260, 274, 275, 293, 302 in order.
To program the remote. Turn on your TV manually and press PGM (to the left of the zero in the number pad section). The LED should light and stay lit. Type in the first 3 digit code and press OK (in the center of the arrow keys near the top). See if the gray volume up/down keys work to change the volume. If it doesn't work press PGM again and enter the next code.
Note that the converter box remote will only turn on and off, switch the input from Channel 3 or 4 to AV in, adjust the volume and mute the TV. It will not control any of the DVD functions. Your original TV remote will not control the converter box.
The manual for the DTA800B1 is available here: http://www.1800customersupport.com/productdocuments/DTA800B1_RCA.pdf
I hope this helps.
(who has the DTA800A which is the model without the analog pass-through.)