Comparing my Shanling M9 Plus to my Holo Bliss KTE + Holo May KTE + HQPlayer when used with STORM, I will note the following.
The Shanling M9 Plus is a warmer DAP and perfectly suits my tonal preferences in when paired with STORM. This pairing is excellent, probably my favourite alongside the iBasso DX320 Max Ti I was able to demo.
Holo stack results in a more neutral, flawlessly clean tonality throughout, never warm yet also never bright. Needless to say, the technical department of this pairing is phenomenal in all aspects, whether that be resolution, staging in all three dimensions of height, width, depth, dynamics and just overall control of the IEM. This easily surpasses any portable chain I have tried, and one would expect it to do so.
However, the degree of which these improvements exist aren't exactly blowing me away either. It's just not the same kind of difference in experience that using headphones on various setups has brought about. It certainly is a noticeable improvement, but I personally don't think using a desktop system for IEMs in general is worth it unless you also have headphones to pair with. It might also be worth noting that a lot of desktop amplifiers may have noise floor with IEMs, though STORM most likely won't have this issue. The dead-silent ones for most IEMs that pop-in mind immediately is Singxer SA-1, Sparkos Aries, and Holo Bliss. STORM on the M9 Plus is already making me more than happy enough.
When I was able to demo the Mass Kobo 475 with Shanling M9 OG and M9 Plus and there was a noticeable difference. Sound was unbelievably clean and neutral, you can immediately notice just how uncoloured the amp was, this was definitely the biggest standout. Dynamics were also improved and it also felt like there was a touch more treble. I don't really recall much about staging or other technical aspects, but given my memory of this was vague and didn't leave an immediate impression, I interpret it as being OK. The overall experience wasn't as mindblowing as it was hyped up to be from all the feedback and reviews I have been seeing regarding the device, and I think my expectations were far too high, expecting desktop system levels of performance. I will give it another go in a few weeks and re-confirm my thoughts though. I have no doubt this is one of the best portable amplifiers around however.
I did notice quite a difference between using Mojo2 with a 4.4 adapter for STORM versus adding a Cayin C9 into the chain, but with that being said, the Mojo2 does have quite poor amplification, and I will re-confirm how Cayin C9 influences the chain with M9 Plus soon.
TL;DR : Does the amplification make a difference? Yes, most definitely. Was it life-changing compared to STORM being driven off a flagship tier DAP and a must-have? For me, not necessarily. However, this is where I have to use a term I dislike : YMMV. To some, the differences between cables and eartips can already make-or-break their experience with an IEM, so obviously amplification matters are a no-brainer. Obviously at this point though, we're all aiming to gain maximum performance from our gear, and with this in mind then a portable amplifier is definitely recommended, though do consider the associated portability issues and if you will actually get the opportunity to use it.
Also on a side note, call me crazy, but the Thieaudio V16 Divinity is the most scaling IEM I have tried, in the sense that the sound drastically changes depending on source. Having tried it from gear like iFi Go Blu, FiiO BTR7, to mid-tier equipment like Chord Mojo2 + Poly, and also desktop gear such as Holo Bliss KTE, Holo May KTE, Burson Soloist 3X GT, Sparkos Aries, Chord Qutest & TT2, the amount of difference between each system is truly night and day. Now I'm sure the mid-tier and below equipment can't even give STORM the proper power it deserves, but you'd imagine an ultra-sensitive IEM like the Divinity to quickly max out, yet I had second thoughts about selling my V16 Divinity when STORM arrived having heard Divinity off Bliss + TT2. I couldn't believe I was listening to the same IEM. That being said, I just couldn't see myself using it with STORM present and using Bliss + TT2 to run Divinity is quite overkill...