I've owned both the USA Trains F3, A & B and now the LGB F7 A and B. I have moved away from USA Trains, although they are wonderfully detailed and run well because the rest of my roster is all LGB. The difference between 1:22.5 to 1:29 was rather noticeable, especially in the locomotives.
In May, I picked up a used F7-A Santa Fe unit in the red Warbonnet trim and just last month a new matching F7-B unit so that I could use the sound. The sound will run in DC analog with a minimum of 6.5 volts on the track. it's simply amazing how well it sounds from the horns to the turbo and powering up. With judicious use of the throttle you can get the sound to start before the locomotive starts moving. (I have a home-built dual 10 amp 12/24 VDC power pack).
Interestingly, both the A and B units are dated 1988 on the undercarriage and state "Made in Germany" and they are quite convincing.
There are two cables provided to connect the two units. There is a 2 pin and a 4 pin cable with a volume pot at the rear of the B unit. The cables provide track power to the B unit for sound and also turn on both the A and the B speakers.
I highly recommend the LGB F7's but make sure that you get both A and B so that you can enjoy the sound. As a side note, there are many other sounds inside of the B unit that could be utilized with a DCC layout, but with 12 locomotives, I'd have to mortgage the house to change over. Since I'm not very good-looking and have few friends, DC is OK for me. LOL.
P.S. These units are apparently no longer made and if you have DCC, make sure that you obtain the correct part numbers for your system.