The `premier' `mod' would be to install an OptoScan OPTO/456 board but, I don't even think that you can find even the OPTO/456 Lite version anymore these days without buying a whole radio/board setup used. The next best `mod' would be to bring out a tap for the `IF', or `discriminator', as that would allow you to be able to some of the various programs that use that as an input.
There really aren't any more `diode' `mods' beyond the `un-block' `mod' that are really all that worthwhile with a PRO-2006. However... *If* yours happens to be one of the older ones that doesn't have the backlight on/off feature I'd heartily recommend that you do the `mod' that gives you it. While I've heard that some people have been able to get new ELP backlights for their 2006s *I* haven't found any myself that were really as good as an `original' backlight. (I *have* done a couple 2006s with LEDs and some very thin `Lucite' panels. Finding the *right* LEDs, they have to be the right size, shape, and sufficient brightness, can be a real PITA as you have to be able to `couple' them to the `Lucite' just right to get good transfer of the light and you have to be very careful to keep all the sides of the `Lucite' panel polished whilst getting the `difuser' side properly frosted. However! When you get it done right the effect makes the old ELP backlight seem like a candle by comparison! [After seeing just how much more readable the newer GREs, PRO-96/2096 and PRO-97, are with their `amber' lighting I am sorely tempted to try and see what it will do for a 2006 as soon as I get moved and my `workshop/lab' set back up! It'd be kinda neat having my 2006s sitting there glowing `amber' just like my PRO-96/2096s, PRO-97s (And hopefully PRO-2055s!), and ICOM R75s! (I *might* also take a shot at `modding' my PRO-2067s and MS-200, too but, they're a bit further `down on the list' so to speak. {WAN GRIN!})])
I've also seen people add `S-Meters', `Tuning Meters' and some other `wild' things that while they might be `sort of' neat *I* have never really seen any use for them. (I'll probably get a lot of arguments for saying that but I'll stand by it. They just really don't do all that much.)
Oh, yeah... There was one other `mod' out there that was kinda neat also. It was called the HB-232 later CE-232 if I `disremembers prezactly I think?'. {
VB GRIN!} It was supposed to allow one to program the scanner's banks and channels from one's computer. I `beta bashed' the `original' one for Bill Cheek in a PRO-2004 and while it did what was claimed it wasn't for the `faint of heart' to do. One had to do some *serious* `hacking' inside the unit and then some more serious `hacking' to get the software to run right. (I'll give Bill due credit as before he died he *did* finally get it running fairly well and there are still a few of his units still out there and being used. But... Like I said... It *wasn't* something for the `faint of heart'! [It *was* however very much `vintage' Bill Cheek! R.I.P. Bill! I *still* miss those times down at your place in North Casper and all the `stupid' things we did to our CBs and the other radios then. {WAN GRIN!} Hoisting a glass of good single malt scotch!]) My 2004 that had it in it died of `old age', I ran it 24/7 since the day after I bought it which was about a month after they came out, about 3 - 4 years ago. It's `mate' died about 6 months later which was not too surprising since I bought it about 6 months after I bought the first one and ran it just as hard. {GRIN!} Even *with* all the solder joint problems and such *those* 2 radios were danged good radios! It remains to be seen if GRE will be able to ever build another `super radio' along the lines of those, 200x series, again.
Just an `Olde Fart's' 2¢ worth. {GRIN!}