How are the sounds of these 3RD RAIL engines compared to the legacy sounds of Lionel?
This can be a point of debate... depending upon whether you prefer absolute fidelity to the prototype or a bit of "artistic license" in favor of great sound. From what I understand, we're at the mercy of ERR on the sound front. And Lionel tends to license "n-1" or "n-2" generation sounds to ERR -- instead keeping the ultimate locomotive sounds for its own Legacy brand products. Here's a link to current ERR sound boards via locomotive series... and you can be the judge.
http://www.electricrr.com/purchaseRailSnd.htm
Some are real winners , and some leave a LOT to be desired . The SD-series and GP-series sound boards seem to have great presence. So folks planning on getting an SD40-2 from 3rd Rail should be quite happy.
OTOH, I find the sounds of the E8/E9, F3, and FM-series locomotives to be somewhat lackluster (based on the sound-files featured on the ERR website). I have two 3rd Rail Canadian Pacific E8's on order from last year, and the word is production has slipped to 2017. I'm OK with the slippage, but please, please, PLEASE 3rd Rail... PLEASE choose a diesel sound package with modern-day presence. It's time for these companies to retire the "sick cow" diesel horn sounds once and for all -- whether it's prototypical or not. Other folks may have different opinions on the matter, so YMMV.
David