I have some experience in growing Acer palmatum from seed.

Root rot is usually the consequence of keeping seedlings too wet (overwatering). Compost should be moist but also well draining. I haven't any first hand experience with pine bark based sowing compost but maybe it holds just too much moisture which leads to root problems for young (vulnerable) seedlings.

I use a professional ericacious potting compost (not available in shops) to which I add some sharp sand (in some countries this is called 'buider's sand'). How much sharp sand do you add? Can't exactly say but not too much or you sowing compost dries out too quickly. Alternatively you can add perlite but this is more expensive and not always available in garden centers.

I wouldn't be too bothered about the acidity of the sowing compost: good drainage is much more important.

On sowing Acer palmatum:

-- First soak your seeds for 24 hours.
-- Japanese maple seeds need 2 to 3 months cold before they can germinate.
-- Reasonably fresh seed usually germinates in the first spring after sowing; old, dried out seed may take a year longer (or might not germinate at all).
-- If you have plenty of seed available you can do a 'cut test' to get an idea how high the percentage of fertile seed is.
-- If you live in an area that doesn't have real winter temperatures you can put the seeds with some slightly moist (= not wet) sowing compost in a ziplock bag in the fridge (NEVER the freezer) at around 5 C./41 F. After two months check regular for signs of germination as Japanese maples can germinate (root emergence) in the fridge. When you see a root appear you can sow them in a pot.

This post was edited by GardenPrince on Fri, Jan 30, 15 at 3:39

Hi GardenPrince, many thanks for your useful info and posts, it is appreciated. I will try to find some Ericacious seed compost here in Melbourne area, but I know I have seen the Perlite, in a 5 Litre bag for around $9 AUD. The Bunnings DIY stores here have quite a lot of gardening stuff. They DO sell some professional grade Osmocote seed raising compost here:
http://www.bunnings.com.au/osmocote-10l-professional-rose-gardenia-azalea-camellia-potting-mix_p3020060
so if you think that slightly acid (PH of around 6) should be good, mixed with a bit of pearlite, I will give it a go when I get my new batch of seeds arrive any day soon.