@ pequenin:
Thanks for all the input you gave on this various keyboards.
From what you are saying about the Casio MZ-X 300 keys, this is a confirmation of what I thoughtt: although it has numerous features, the build quality of this Casio is not so good. So I will not be considering the Casio any further. Also you are saying that the synth sounds are far better than on the Yamaha but I am not that interested in synth sounds, I am more looking for nice acoustic sounds for pop, jazz, film and Classical music. For instance I find that the Sweet! Classical flute is a nice addition to the sound palette of the PSR E453 (I have noticed that I have been extensively using the Sweet! and Cool! sounds of the PSR E433 when I had it and of the DGX 650).
I looked a bit at the specs and if you need modulation and nice guitar sounds, the Korg PA 300 might be what you are looking for, excepted that opposite to the Casio, the Korg unfortunately won’t read Yamaha styles. But all sounds and styles are fully tweakable, you can even edit your own drum kits. Here is the commercial video made by Korg when the PA 300 was released: IMHO the piano, guitar and synth used in the video sound quite well (but this guy knows how to play an arranger keyboard obviously).
https://youtu.be/bR4mhYFteSYMaybe you can try the PA 300 somewhere before deciding between it and the PSR S670?
And if you really are missing the Mod wheel on the PSR E453, the Yamaha SoundController app for iPad might be what you are looking for. You can download it from the AppStore. It gives you a Pitch-Bend wheel and a mod wheel on your iPad. You simply need to connect your iPad to the keyboard via a USB printer cable and Apple Camera Connexion adapter. I have done it with the DGX and it works flawlessly.
As for your offer of buying your PSR E453, I am considering it but my choice is not made yet. If I go for it I will contact you through a private message. This is also a difficult choice because for the time being it would be very difficult for me to go to a music store and try the various instruments I have in mind. So it might be better for me to buy a new instrument on Internet so that I can send it back if I don’t like it.
As for the speakers is is not the main issue for me. It is always possible, when needed, to work with headphones or a PA system. There is also the possibility of using the speakers of my DGX 650 as the sound output for the second keyboard, since the DGX fortunately has an Aux In socket.
@ Panos: It is true that the PSR S series is one step above the E. But newer E keyboards might have features that older S keyboards don’t have, like the Audio USB for instance, or new styles. USB audio is great because it works both ways: for instance, you can connect an iPad to a PSR E453, launch the Korg iM1 app, and you have a Korg M1 in your PSR E453! See this video:
https://youtu.be/G8Cj7T8aaJoWhat was great with the PSR S650 as opposite to the PSR E series was the possibility to add new sounds and styles. The Church Organ pack was esp. nice IMHO. Great for organ lovers on a budget.
Best Regards to all,
Vinciane.