One more note regarding the different application modules for the TDS3000x series.
As far as I know, Tektronix only ever sold the following EEPROM application modules:
TDS3TRG, TDS3FFT, TDS3VID, TDS3TMT, TDS3AAM, TDS3LIM.
As mentioned earlier in this thread, TDS3TRG and TDS3FFT are enabled by default with the later firmwares. Thus, together with a home-made TDS3AUM EEPROM module (described in the OP), one gets all the modules ever sold by Tektronix.
The TDS3ENG engineering DIY module mentioned in this thread includes in addition TDS3BTA, and TDS3SDI which do not correspond to any commercially available EEPROM module ever sold. As far as I can tell, these are debugging/repair aids used internally by Tek.
The TDS3BTA stands for "Beta functions", and nobody seems to know what these are, if any. If anyone knows more, please share!
As for the TDS3SDI, there was a module sold by Tek. with this name, but it is not an EEPROM you plug into the slots at the front right of the instrument. Rather, it is a big hardware module one plugs in the back (like the Ethernet/GPIB/RS-232/VGA communication modules --- see attached image). According to its manual it: "...converts serial digital video to analog video composite and component (RGB or YPbPr) signals connected to the oscilloscope inputs". Like most modules that plug in the back of the scope, this module also adds items to the instrument's menus. The TDS3ENG EEPROM adds the same items to the menus (e.g., QuickMenu->Video->SUBMENU: ITU-R 601), however, without the hardware of the real TDS3SDI module, this seems of very little use.
In short, if you have the latest firmware, I see no advantage of the TDS3ENG module over the TDS3UAM module. In fact, the TDS3ENG has the disadvantage of showing me an annoying warning on every startup, which the TDS3UAM does not.
Thus, my recommendation at this point (unless new information comes in) is to forget about the TDS3ENG EEPROM, and stick to the TDS3AUM.