for me, balance i put neutral while Fade setting i set R +2 giving me more bass from my rear channel using 6x9

Nope, i use fading via HU. No amp yet.

I'm using Pioneer DEH1550 with just one Rear RCA pre-output.

Should i invest in cheap pre-amp or cheap electronic x-over?

Which is better?

Once i use this pre-amp/electronic x-over, do still need to fiddle my Pioneer EQ setting?

Actually, get a cheap amp, cheap speaker and most important is better than your Myvi stock speaker. Is worth to get it. Besides not everyone are rich to spent more than their budget range and not everyone wanted pure high quality sound system.

Why will there be lower end version of sound system in the market? Is meant to enjoyed by everyone who is seeking a better system than stock does.

Here is my point of view for your Myvi system.

1. 4" 2 way speaker from Soundstream Xstream model roughly rm 150 to rm 200

2. 12" subwoofer range from rm 300 to rm 350. branded like JL Audio, Soundstream,

3. electronic crossover 3 way RM 200 to rm 250

4. wiring kit, 2 pairs of rca cable, fuse box, amp power cabling RM 150

5. Caliber Ca-5000 4 channel Amp get from auction roughly RM 300 ++

Your system should at least better than stock rather commented being sounded like shit.

Then those soundstream barring with MAT sticker at low price is fake then?

is advisable to seek ICE shop for installation. You need to know how to remove the front dashboard speaker grill to replace the 4" speaker.

More ideal would be installing a component speaker for your front sound speaker. Get a component set with tweeter and crossover. Size will be 6.5" to enjoy good music because 4" 2 way and 6.5" component set is not much different in price. Install the tweeter in your 4" speaker space while the 6.5" mid bass at your door with custom made speaker bracket.

Then you won't felt shitty sound system as the high (voice) can hear singing in front of you while the mid at your side. But this setup is more like a sound staging.