Have an '01 A6 2.7T TIP 110K miles that I purchased brand new. Always wanted to mod, but never got around to it.
As most know here, just keeping the 2.7T HW healthy can be a challenge. Since my extended warranty expired, I do all work myself:
timing belt kit, sensors, diverters, suspension parts, CV's etc, etc.
I use VCDS all the time (even when it was VAG.COM), so I don't have any outstanding codes. No oil leaks. Turbo's are healthy from everything I can see/measure.
As far as I know, engine has zero issues and is performing as it's supposed to. TIP is "OK" to, but wouldn't be surprised by a torque converter code some day.

My goal is to achieve a reliable/mild stage 1-ish tune. Can only get 91 octane gas here. Want to use stock HW and get a bit more street acceleration out of this nice car without killing mpg while cruising. After popping around this site, I think I know what to do, but still have noob questions. Please excuse me if I didn't hunt these down enough.
1. Car build was 11/2000. How do I know if I have a 2001, or a 2001.5? I know I don't have the "F" hose in front (above the thermostat). Or what box do I have?
2. MAF. Doesn't say Bosch or Hitachi on it.  Just Audi part number. How do I figure that out?
3. Immobilizer. Is it true that any tune I create will have the immobilizer disabled? That may be OK, but anything to be concerned about?
3. Suggestions for a good .xdf to study or begin with for an auto A6.
4. Is there anything in the A6 2.7T that is substantially different than the S4 HW? That is, do I have to look for, or create custom tunes because this is an A6?

I'm blown away by this site. Being a techie/hacker for most of my career, this is a site from heaven.  Can't wait to begin.

Thanks ahead of time for the folks that make this go,
Illbay

Thanks for the concise reply. Some info and yet more questions.
VIN says I have a 2001 model although build date was 11/00.
Went to take pics of the MAF and, duh, it says Hitachi on the side. Was looking at the top originally.
Does the MAF matter or help determine what box I have?

Is is necessary to create new checksums when anything is modified? Seems to me, yes. In other words is a checksum generator essential to do any tune?

Thanks while I spin up?
Illbay

Not true... 2000 MY came with Bosch... my friend has one and we swapped it to a Hitachi.

interesting, I stand corrected then!

Not sure there was a 2001.5 a6, either way there isn't much of a difference between them(tuning wise), I would guess you most likely have a 4B0907551T ecu, but you can verify it with vcds or nefmoto.

And yes you will need to calculate new checksums for any change no matter how small, the plugin is only $15ish so shouldn't be that big of deal.

If you don't mind losing immo, it will make it a lot easier for you to use a common ecu bin(s4 L box I believe is the common tip one).

It's pretty nerve-racking the first few times, personally I've had 2 failed flashes(one my laptop battery died all the sudden in the middle of the flash, the other was some communication error), both times nefmoto was able to still connect and flash a complete bin.  Also pay for the premium features, then you only have 1-3 minutes of stress/not wanting to move or touch anything instead of 10-15 minutes!