It is not entirely impossible, and you can buy appropriate NAND chips from aliexpress or similar chinese webshops. However they will cost around half of what apple would charge + you need proper equipment and handywork to replace and reconfigure the boards. It takes experience to do it, and if you pay someone to do it, you will be very close to what it would cost to buy it directly pre-configured from apple. You can get on with a fast external drive and the smallest amount of SSD like 256 or 512Gb though... Buy as much RAM as you can afford that's more important imho.

You could also try to adjust the potentiometers that set the current strength flowing thru the lens coils. If you make the resistance of the potentiometer 5-10% lower than what it currently is it will probably be more than enough to read your DVD discs. You have to take apart the PS2 then unscrew the 4 screws on top of the disc drive (fat models only). Take heed of ejecting the tray before unscrewing the 4 top screws off of the drive. Then take the rails out (the laser head rests on them) and turn the laser head over. You will see 2 small pots in there. Maybe they have a cd / dvd text written near them or maybe not - the thing is one of them adjusts the current for reading cd discs the other is for dvd discs. If you want to make sure all is good then measure their current values with a multimeter and take note of it. Then subtract 5% first from both of them, adjust, measure and put everything all together. I think the screw needs to be turned anti-clockwise to lower the value. It should work; but if it...

You have to have a jtag'ed xbox 360 for the optional media update to be usable on a box that's not the one on which it was downloaded. in this regard it's a pain in the $$^ and the ps3's media capabilities are better without any 'optional' stuff