It looks like Target Disk Mode is actually a viable solution if you have another Mac.
I'm going to try this out tonight as soon as I get home and will report back if I can get it working.
After struggling for several hours last night I'm still stuck with Lion. :/
I tried target disk mode a few different ways and every time results in a kernel panic. There's something going on with the hardware that refuses to be downgraded.
At this point my only recommendation is to hold off on the new Mini until an update is released for Lion. I know that a few people are reporting that their experience has been positive, but for every one of them there are dozens experiencing problems. I have had to hard reboot this Mini ~50 times in less than a week. I've even gone as far as having Apple replace the hardware and I'm still seeing the same issues.
As always YMMV.
For those desperate to try this, the answer is simple: any existing / older operating system release simply does not have the proper drivers to support the new hardware (motherboard, chipset, cpu, ...) It will panic.
This is even the case with mid-cycle releases; where new notebooks & desktops were released with for instance 10.3.5 - 10.4.7 - 10.6.5 (numbers just as an example). If on those systems you need to do a clean install, don't have the factory discs that came with the unit and think you can just use the previous OS or the official upgrade disk to 10.3 10.4 10.5 or 10.6 respectively ... and then update back to 10.x.x ... you cannot. The earliest OS that works on any mac is that which it was released with.
There are instances where one can cross-boot so to speak with another drive from a similar generation ( PPC or Intel ) machine with the same OS version. But that is different than installing the previous OS.
Not to be that guy, but you're wrong.
The latest hardware CAN run previous versions of OS X under a very specific set of circumstances (like what we have here). If a new MBP is announced mid-cycle you're right, it cannot run a lower version than it was released with.
However in the case of the upgraded hardware that coincides with a new OS release (not an upgrade to existing) it's more complicated. Snow Leopard 10.6.8 can run successfully on the new MBP/Mac Minis. I know this because I can put my MBP (10.6.8) into Target Disk Mode, connect it to the Mini and then boot that drive on the Mini. So 10.6.8 is running on the Mini's hardware without kernel panic.
The issue that is left unresolved then is getting 10.6.8 onto the Mini. You cannot use the Retail SL installer because at best it's at 10.6.3 which, as you've pointed out, lacks the drivers to handle the latest hardware. I was hoping that I would be able to install SL onto the Mini running in Target Disk Mode without issue, then immediately run the Combo Update for 10.6.8. That should work in theory, but unfortunately doesn't in practice.
So I'm left with one final option which is to pull the hard drive entirely and swap it with another 2.5" SATA drive which does have SL 10.6.8 successfully installed on it. My biggest problem there is that I've only had this thing for 6 days at this point and swapping the drive out this soon isn't really something I'm looking forward to.
After 6 days and NUMEROUS attempts I have figured out how to get Snow Leopard onto the new Mac Mini!! It turns out I wasn't thinking the problem all the way through. I thought that the Mini was causing the kernel panic when connected in Target Disk Mode. However I was trying to install the retail Snow Leopard (which is 10.6.0) onto the Mini using an MBP which required 10.6.3!
There is a step after all of the applicable files are copied to the Mini (TDM) where the Source machine reboots and is supposed to continue the install. This is where my MBP was freezing up and I couldn't understand why. Well it turns out that the MBP is attempting to boot from the SL disk (10.6.0), however this machine requires a minimum of OS X 10.6.3 so the boot was hanging.
I ejected the retail version of OS X, input the Recovery disk I got with the MBP (which is 10.6.3) and the install continued as usual. Once installed I booted directly to the Mini's hard drive (TDM) via the MBP and ran Software Update to get to 10.6.8. Then rebooted and let the Mini boot itself...and we're up!
1) Put Mini in Target Disk Mode (Firewire only)
2) Put SL retail install disk into Host Mac and install to the TDM drive
3) When the reboot hangs power the machine down (or if you're fast hold down Option on that reboot) and restart holding Option.
4) When the boot choice screen appears eject the Retail disk and input your Recovery disk.
5) Boot to the Recovery disk and the install picks up automatically (don't worry, it's actually installing 10.6.0 even though you're booted into 10.6.3's recovery).
6) Once you've gone through the new user introduction stuff (input username, etc) run Software Update
7) Power down the Mini and restart it w/o TDM.
Now -- can we hide this whole thread about your finding an answer? Just joking, Apple -- I've had Macs since 1986, and I know that you'd never put your customers in a bind like that!...
This makes the 2011 Mac Mini so very, very, very much more useful to me and to so many others! Just read the online whine in so many forums! As soon as I can confirm that we don't lose some drivers for the AMD Radeon GPU, I'm onboard with an immediate order for eight 2011 Minis with i7 duos and the Radeon HD 6630M. Happy face!
Quite a few of us need some of the capabilities of Snow Leopard that are (for right now, anyway) lost in Lion. Soon, soon, we can no doubt upgrade to Lion as the gaps are filled, but for now -- nice machine, elegant Lion, imperfect combo for lots of real-world work. For now.
Anyway, great work, John! A primer in how not to give up, but keep poking 'til you get it right. I've been following your thinking (and that of others) who reasoned that very similar hardware might be able to run the same OS, regardless of box. QED!!! Yea!