Hello Dwaeji - you can use inversions of C major? That is C,E, and G to start, then move up to E, G, and C, then up again to G, C, and E, then you're back to C major an octave higher. Sort of fills in the gap..

This is the Montage section, so details for the PSR-E443 are going to be hard to come by here. Before this message gets transferred to some other section, I'll give it a shot.

I would split my keyboard first, then adjust octaves of the split.

For the split, see:

https://www.youtube.com/watch?v=OnL7Vru2Q14

For octave adjustment, see:

http://faq.yamaha.com/us/en/article/musical-instruments/keyboards/digitalkeyboards/portable_keyboards/psr-e443/10793/2603/I-ve_made_the_split_keyboard_settings_now_how_can_I_raise_the_pitch_of_the_left-_hand_voice_an_octave/?current_page_id=1&sort=&type=

I'm not sure if you can assign the same voice for both sides of the splits - that's how I would try to do it. If not allowed, I'd pick two voices which are close variants like Grand Piano and Bright Piano. Or Hyper Tines and Funky Electric Piano. Or Cool Organ and Click Organ. You get the idea.

This is a way you can get the left hand and right hand playing the same octave - or keep the 24 notes centered around the split point (F# by default) within the same octave.