What can I bring legally from USA?

The first question should be - Will they work.

The US has a 110V system and most equipment there seems to be supplied with 110 only power supplies, but Malaysia is 220v, meaning some of your equipment may go bang as soon as you plug it in.

Your next question should be about import duties and would it be cheaper to buy new rather than ship and tax.... and buy transformers to sort out the compatability problems.

Good questions.
1 I am aware of the voltage differences so I am bringing some voltage converters.
2 Am I obligated to pay import tax on the used household goods?
3 Do they waive any taxes for MM2H visa holders?
4 If I am allowed to bring my own used goods, how do I prove they are used if I don't have the receipts?

Thanks!

Tech again. Many converters are limited in wattage so make sure the capability of the converter is at least 1.5 times your requirements.
Quality HiFi will need a smooth supply and many converters are square wave rather than sine, so be careful to check first, then test before moving.
Things like laptops will usually take anything you throw at them.

Customs  waives duties on all household goods purchased more than Three months before for MM2H holders. You also cannot dispose of the items until three months have elapsed from their importation. At least that is what all agents web sites state. I cannot find any such statement on the official MM2H website. Maybe someone else has the appropriate document.

Make sure a copy of your passport particulars page and MM2H Visa are prominently placed in the shipping papers. Not sure about other visas. In a clinch append this to the documentation. https://www.mm2h.com/customs-importing- … -malaysia/

Old model computers should be fine...maybe slap a few peel-off stickers on the laptop to make them appear suitably used. Remove recently purchased items from original packaging OR make sure receipt or other item dating the item is on the outside (more than three months old). 

Here are some typical household items.
o Crockery and cutlery
o Furniture
o Beddings / curtains
o Pictures / wall paintings
o Kitchen electrical such as kettle, microwave
o Garden appliances such as lawn mower
o Electronics appliances such as television, radio or DVD player

Items Not Categorized Under Personal Household Effects[These are dutiable]
o Motorbike
o Car  [Until 2017 a used car was not dutiable but that benefit has been eliminated]
o Powerboat
o Yacht
o Motor home / Caravan

List of Prohibited/Restricted Goods
o All types of Piranha fish; turtle eggs, cocoa pods, rambutans
o Dagger, flick knives;
o Broadcast receivers capable of receiving radio communication within the ranges
(68 – 87) MHz and (108 – 174) MHz;
o Cloth bearing the imprint or duplicate of any verses of the Quran
o Pen, pencil and other articles resembling syringes
o Poisonous chemicals
o Lighting arrester containing radioactive materials, etc.
oLive animals-primates including ape, monkey, lemur, galago, potto, and others.
oExplosives and Fireworks
oImitation arms, toy gun / pistols/ hand grenades.
oArms and ammunition other than personal arms ammunition imported by bona fide traveler.
oBullet proof vests
oLive pests including live insects, rats, snails, and cultures of plant disease causing organisms.
oBatik sarong.
o Apparatus/equipment for the brewing of beer in the home. !!!
o Electric domestic equipments that use 50 volt or 120 volt Dc or more

Amongst other interesting items....Full list here
http://www.customs.gov.my/en/tp/pages/tp_ie.aspx

Great tips! 
That gives me things to research and test out.
Many thanks!