Moving to Singapore. Help needed

I appreciate some help with my present situation.

I will be relocating to Singapore later this year, and was advised several times that speakers, receivers and amplifiers are SIGNIFICANTLY more affordable in the US. As shipping will be borne by my company, I wonder it'll make sense to assemble a set here and ship them over. I understand the electrical system is different in Singapore (220-240v), compared to 110-120v here.

My specific questions:
1. Is it possible to get 220-240v amplifiers/receivers in the US? Is there any specific brand that either carries models that support the 220-240v or allows one to tweak 110-120v to 220-240v easily? I am not very keen on a transformer, as they are generally bulky and will avoid them if I could.

2. Do the differences in electrical supply have any bearing on the performance of speakers?

3. I understand Iphone/Mac users can stream music to their receiver using AirPlay or adding an Airport Express; so far only Pioneer supports AirPlay (as far as I know). Is this true? Is it possible to play music through my Iphone/Ipad/laptop on these systems with no AirPlay compatibility? Appreciate if you could share some of your experience here.

4. An 804 diamond currently retails at $7500, while used 804S and 804d are selling for much less. Is the price difference really worth the sound quality? I spend time listening to vocals, jazz and instrumentals.

Many thanks for your time to ease my audiophilic dilemma.

SP