diferencia en el HARDWARE de la pantalla: (texto obtenido en review de mobile reviews)
Having opened the device, you will face the internal display, with a resolution of 128x160 pixels, armed with UBC technology (only applied to Z530i, but not featured in W300i). This is a kind of replacement for UBF, which, in its turn, relates to STN-matrixes line-up. The new title of the technology in this handset is aimed at stressing its superiority over STN-matrixes of the previous generations in terms of contrast. Of course, the colors, reflected by this display are vivid, but it yields to the majority or qualitative TFT-screens, as it has distinguishable pixel size, and it’s no wonder, considering the resolution. On the whole the display performs well, even though sometimes it fades away in sunlight, information remains readable. The screen is capable of displaying up to 65 K colors
W300i has the same display incorporated, though the technology used here is TFT, and what is more, it can reflect up to 262 K colors. The better display is explained by higher positioning of the device. The overall picture quality here is a bit better – pixels size is not so obvious here. At the same time, for this price bracket and class, the screen is quite average, since it may be referred to the previous generation due to low resolution
basicamente, ambas pantallas tienen la misma resolucion, pero usan diferentes tecnologias, la del z es de 65k colores, la del w es de 262k colores.

aca esta la review (esta en ingles, pero bue)
http://www.mobile-review.com/review/...-z530-en.shtml

en cuanto al reproductor, es un hecho q NO es el walkman player, pero como nunca vi el celular, solo puedo comentar:

si es como el q tenia mi z710, es CASI igual, solo q carece de la opcion MEGABASS en el ecualizador (es casi obtenible ecualizando a mano), y cuando estamos en la pantalla de "reproduciendo ahora" NO se accede a la lista con las flechas arriba/abajo del pad direccional. (en el walkman player si).

si el reproductor es como el del k790, es identico al W salvo por los colores y la ausencia de megabass.

si el reproductor es como el del z520, es mucho muy inferior al walkman :P

lo demas q viene EXTRA al celular, se puede comprar aparte, a mi no me gusta q me cobren extra por una m2 de 256 megas, q para mi es diminuta.