PAL on A2000HD?

[Oldsmobile_Mike]

Assuming you have at least Kickstart 2.04 ROM's you should have an early startup menu.  However if your 2000 has an early model Agnus (8370, 8371) it may not be switchable to PAL.  You'd need to upgrade that.  The 8372A is a drop-in replacement for most motherboard models that's pretty easy to source (came in most later model A500's/2000's), and would allow you to do the chip ram mod (1MB chip ram instead of 512K chip/512k fast), as well.

https://en.wikipedia.org/wiki/MOS_Technology_Agnus

AFAIK shouldn't be a problem using the splitter cable to join the audio channels, but it's been at least 20 years since I've done that.  Might want to wait for a better answer, on that one.

As an alternative, I'm sure your local craigslist has plenty of cheap-o stereo receivers that you could hook up for real stereo sound.  That's what I always did, back in the day.  

[Oldsmobile_Mike]

So 3.1 is still going to keep the 2000 compatibility for games? my 4000 sucks for playing games because of the faster CPU and other issues. I bought the 2000 for my kids to play these classic games on that wont run on my 4000.

I know I sound like a broken record here, but why don't you just use WHDLoad?  Although if you really want a "classic game experience", go back to 1.2 or 1.3, lol.

Also, I don't think the Amiga mixes audio channels. Plug in one channel, you'll get one channel. Although maybe something newer (like a 4000) would do it.

[Oldsmobile_Mike]

Yup, plan on installing that but need to get a cd drive in that a2000 first as the LZH file of WHDload is too large to fit on a floppy.
The kids are not allowed to use my 4000, it's off limits.

Whdload_user_small on the official website is only 684k and contains everything you need. If you really want to strip it smaller just grab the C:Whdload executable and ramdic, and the couple other executables in the archive. The rest of the size is just documentation.

Easily transferable on a floppy.