@deepanker100,
Hi again. Thanks for your response and questions. Ultimately, I think your SoundTouch 300 and potentially your TV might get in the way to achieve multichannel LPCM. Let me explain why.
Your SoundTouch 300 - Lack of e-ARC means you will be limited to uncompressed LPCM 2.0 and/or lossy multichannel formats like Dolby Digital 5.1. That doesn’t mean you are getting inferior sound quality. But the short answer to your question is, yes, most likely Atmos content will be down mixed to Dolby Digital or LPCM 2.0 depending on your settings since standard ARC doesn’t have the bandwidth capability e-ARC offers. Also, I wound’t necessarily call it “downmixed” since the soundbar does not actually downmix anything. It outputs the highest quality your sources provide. This can depend on HDMI specs of your devices, cables you use, settings on your devices, and the sound formats your sources support. I personally prefer Dolby Digital 5.1 over LPCM 2.0 even though technically DD 5.1 is a “lossy” format and LPCM is an uncompressed format. I find the bass to be punchier and the surround speakers to be more prominent with DD 5.1. May be some music may sound slightly better with LPCM 2.0 but I do prefer the wider soundstage of DD 5.1 decoding. It’s a different story when you hear LPCM 5.1 or LPCM 7.1. Simply sound superior over DD 5.1 or LPCM 2.0.
Your TV - This one is a bit more confusing. Unless you bought your TV in the last year or so, chances are it may not actually be able passthrough multichannel LPCM despite the fact that it may passthrough Atmos. This will all depend on your TV model and HDMI specs. You specifically need HDMI 2.1 ports and e-ARC compatibility. For whatever reason, TV manufacturers were not allowed to passthrough uncompressed multichannel formats until very recently. Rules were not strictly enforced though which is why some TVs incorporated the function while others didn’t. One thing to keep in mind is HDMI ARC can receive Dolby Atmos audio as the format is embedded in Dolby Digital Plus which is still a lossy format unlike LPCM 7.1.
Here is a link explaining differences between ARC and e-ARC. There is a helpful chart too.
https://www.cnet.com/news/hdmi-audio-return-channel-and-earc-for-beginners/
That said, upgrading to Apple TV 4K (2nd generation) will very much improve your overall experience - both visually and sound - since Apple TV uses superior hardware, silicon and optimized for best experience even if your current setup may not allow you to get multichannel LPCM. Dolby Digital 5.1 quality can vary also depending on where or how you are watching. I had Comcast cable not too long ago which supported Dolby Digital 5.1. It was nowhere near Dolby Digital quality I would get from Apple TV , Netflix or Amazon Prime Video. One would assume they should sound the same but they simply don’t. Anything I play through Apple TV would have a much higher bandwidth which results in noticeably better sound. It does make some difference too compared to Chromecast which I will get to in a bit.
I admit Apple TV is not cheap but anyone who buys one would tell you its worth every penny. UI is polished and smooth, blazing fast, and supported for years. My six year old Apple TV (4th gen) - they call it Apple TV HD now- is still supported with the latest OS updates and features and will be supported for at least another few years until the hardware can’t handle the updates anymore. Now that I have the latest Apple TV 4K (2nd gen), I use it in the guest room. Both run on latest OS but obviously the new one has all the hardware upgrades.
Simply put, your best bet is to buy the new Apple TV 4K and figure out if the upgrade is worth it or not. I am confident you will find plenty to like about Apple TV 4K, speed and extensive support being major advantages. One of my friends gifted me a Roku stick last year. I thought it was terrible. I borrowed a Chromecast from a friend also and quite frankly didn’t meet my expectations. Both Roku and Chromecast capped at 92 mbps on my network which is equivalent to my six year old Apple TV. The new Apple TV 4K goes all the way up to 320 mbps which makes sure I get the highest bandwidth for both audio and video. Obviously this depends on your internet speeds in your home but still a pretty big difference in terms of antennas being used in these devices. Overall UI and speed was quite a downgrade for me also; especially with Roku since I am used to super fast and smooth UI. You may have a different opinion but if you decide it’s not worth it, you can always return it. I believe you have 15 days to return it for a full refund. It’s the cheaper than upgrading your soundbar or TV.
I hope this was helpful without being too confusing 🙂
