I ran a google search to check for more detailed specifications of your HTIB system, the Sony BDV-E490 so here's some specs...
1 x HDMI Output
1 x USB
1 x Composite Video Output
1 x Optical Audio In
1 x Analog Audio In
1 x Ethernet Connection
1 x Infrared InMmm... you DO have a problem to connect Byond HDMI to your system.
From your reply, you can only use...
(2) BD Home Theatre to HDTV via HDMI for both audio and video without spending extra $$ to purchase converter. Can also use Byond RCA (red, white) to your Sony BDV-E490 but only PCM stereo 2 channel audio.
The Sony BDV-E490 blu-ray player have the amplifier built-in. This stand-alone blu-ray/amp unit is NOT intended for any HDMI devices to be connected to it so ZERO HDMI Input ! Too bad for you.
It also do NOT have any Co-Axial Input.
The coaxial cable used is the same as the satellite cable with 75 ohms. The problem for you is that the Byond box have Co-Axial Output BUT NO Optical Output. Your BDV-E490 have 1 Optical Input BUT do NOT have Co-Axial Input.
First, solve the video connection which is easy. I am sure your HD TV have at least 2 HDMI Inputs. You can use the TV HDMI 1 connect to your Sony BDV-E490, and HDMI 2 connect to Byond. Done for video.
For the audio... bad news because you CANNOT use either the HDMI or the Co-Axial outputs from Byond connect directly to your Sony BDV-E490 to get Dolby Digital 5.1 audio.If you use the Byond RCA (red, white) connection to your Sony BDV-E490 Analog Audio In, then you will NOT get Dolby 5.1 ! If you use your HD TV speakers from the HDMI 2 connection, then the audio is lower quality at only PCM stereo 2 channels.If you do NOT want to spend $$ any more, then too bad that you have to accept using either the TV speakers sound or your Sony BDV-E490 stereo 2 channels.

IF you really want Dolby 5.1 to your Sony BDV-E490, then I can
suggest to purchase a Co-Axial-To-Optical Converter which supports Dolby Digital 5.1 such as the
Gefen Digital Audio Translator which costs about US$ 79. Here is the link... "
http://www.gefen.com/kvm/dproduct.jsp?prod_id=9137". This converter accepts audio signal from 2 channels up to 5.1 channels. Mmm... last year I did phone to a local Malaysian agent in Kelana Jaya or Mid Valley but unfortunately I cannot remember much. Mmm... I think its about RM 300 to 400, not sure now. Anyway, you can search the website from the link I gave here to find the Gefen Malaysian dealers.
Of course, you can use other brand Co-Axial-To-Optical converters as long as its reliable, cheap and have quality and make sure it can output to Optical as Dolby 5.1. I hope others here may be able to recommend other brand converters which are better and cheaper, hehe.
I did not suggest using HDMI to HDMI Video+Optical Audio Output converters because these are usually very expensive, maybe between RM 800 to RM 2000 !
Ok... if can get the Co-Axial-To-Optical Converter (support Dolby 5.1 output), then your problem solved...
1) Byond HDMI Out to HDTV
HDMI In 1 for 1080i HD Video.
2) Byond Co-Axial Out to
Co-Axial-To-Optical Converter and then optical out to your Sony BDV-E490.
I do NOT know whether the Sony BDV-E490 support or not support Dolby 5.1 from its Optical In.
IMPORTANT... if Sony BDV-E490 Optical In do not support Dolby 5.1 then forget about the Converter and too bad you have to accept lower audio quality as I have explained earlier.I can understand that you are worried that "you did not make sense" in your post. Don't worry, no problem. Not everyone is good in everything. I am a person who seldom lose temper, try to always stay cool and got patience... and very little sleep too

EDIT : Oh, I am not a salesman for Gefen products, did not say that its products are suitable, good or bad and did NOT recommend anyone to purchase their products... my suggestion only. You can always choose other brands.
Most important now is to get at least 2.1 for Astro Beyond. You mentioned just using the RCA cables which can get PCM 2 channel audio. Is this decent enough? I was using this cable to connect my normal Astro and it didn't seem too bad.
And about the Dolby 5.1 optical in, I've just sent a message to Sony MY and now waiting for an answer
For now 5.1 isn't really that important as my dad didn't even plan to use 5.1 due to messy wires but I will show him a full 5.1, 1080p video later on
Thanks again! Really appreciate your effort to help me out on my question.