Tsunami (obsolete) = 1A (motor), 1W (sound power), 8ohm (optimal sound load) - the original Tsunami, often referred to as "the" Tsunami decoder
TSU-2200 = 2A, 2W, 8ohm - this is of the Tsunami2 product line that obsoleted the Tsunami, but actually the Econami decoders that came after the Tsunami but before the Tsunami2 line pretty much put the original Tsunami to bed, and are also well worth considering (e.g. ECO-200)
Tsumami 4400 = 4A, 3W, 8ohm -- note this decoder is physically larger than the 2200 which serves most nearly every S gauge requirement
There are a considerable number of S engines, including some with smoke and sound, with original Tsunami decoders still in them running around - and well at that. Pretty hearty little units despite their low ratings by modern standards for S purposes. The practice of one decoder for motor, and another for sounds is also outdated by new more capable decoders since the days of that workaround.
Soundtraxx has a very informative web site, their documentation (even for discontinued products) is robust, and their people are very helpful. Oh, and their products work great as well. Assuming you match specific decoder capabilities to your application and needs.
PS I have no affiliation with Soundtraxx. Just success with their decoders, documentation, and staff.