I've never played a Tyros 1. To compare sounds, I'd start by listening to youtube videos. But technically, you can see some differences in the specs that show how many Voices (instrument sounds) they have, of what type...
PSR-EW473: 820, consisting of 294 Panel Voices + 28 Drum/SFX kits + 40 Arpeggio + 458 XGlite Voices
Tyros: 1185, consisting of 403 voices (Normal: 393 + Mega: 10) + 10 Organ Flutes voices + 480 XG voices + 256 GM2 voices + 31 drum kits (XG and Panel: 22 + GM2: 9) + 5 SFX kits
and
PSR-EW473: 3 Live! Voices, 9 Sweet! Voices, 6 Cool! Voices, 14 Super Articulation Lite Voices
Tyros: 22 Live! Voices, 14 Sweet! Voices, 18 Cool! Voices
(Both have about 300 styles.)
But sounds aside, the obvious relative negatives of the Tyros are portability (weight), no styles specifically for anything post 2002 (though I don't know what's available to load into it?), need to use external speakers, antiquated storage, and potential reliability/serviceability for something that old. OTOH, even just based on what I see in the manual, functionally, it is in an entirely different league from the PSR-E473. The screen (much better navigation), the action (with aftertouch), mod wheel, the connectivity, the sequencer, the polyphony, the vocal harmonizer, the quantity of available effects, the more extensive set of intro/variation/ending buttons, the better registration system for quick patch recall (banks of 8 named registrations with direct bank navigation vs. banks of 4 unnamed registrations which can only be navigated in ascending order), 3 upper parts (vs. 2), and as listed above, simply more voices (also the megavoice and organ flutes additions). Though the PSR does have some enhancements of its own as well.
For connecting to a computer, I would not count on any Tyros driver working on any current computer, though from what I saw in the manual, it looks like most (if not all) of the data transfer can also be done over its 5-pin MIDI jacks, and you can get a 5-pin-MIDI-to-USB adapter pretty cheaply.
FWIW, I briefly had the PSR-EW425 (73 key version of the PSR-EW473), and like Bouncingogre, I sold it within a month. I think I'd enjoy a Tyros, though!
If you decide against the Tyros for whatever reason, overall, I think the Casio CT-S500 is a better board than these PSRs, I kept that one. It's not one of my main boards, which are generally higher end, but it still has its uses. Bottom line there is that I find it more enjoyable than the PSR, in playability and general operation. (I never looked at their styles, so I have no opinion there.)
