what JDFlood said is true however the dragonfly is a much better DAC so I would use it and put AUX in the Topping and skip it's DAC capability and use the dragonfly..
So what is MOST important about your headphone after the ohms is the sensitivity, so most passive speakers are 4-8 ohm... but your phone cannot drive these because of sensitivity which instead of db/mW is db/W or db/1000xmW... Your phone can handle somewhere around 32 or a little higher maybe almost around 50 ohm USUALLY but the sensitivity matters if you had a 90db/mW sensitivity I would say your would probably be good but you have an insanely higher 100+/mW sensitivity so there is a very good chance you won't even max out the volume...
so 2 factors play into this, we talked about a more expensive AMP giving more detail and resolution.... this is because a cheaper and worse AMP will take the signal you have (if the DAC is a bad dac the signal will be bad and no good AMP will improve it, if the DAC is good then a bad AMP will not give you all the quality but if the DAC and AMP are good you will have very close to maximum quality from the player to your headphones) So in this case your headphones would probably sound noticeably better WITHOUT the AMP as it could possibly downgrade the quality of the DAC which I believe is a expensive "good" one so likely high quality.... So I would avoid it if it can be avoided, if not you should get it try it and try to see if you can notice a loss of detail, resolution or imaging(being able to pinpoint the sound in a 3d soundscape your headphone provides, with good imaging you will have a clear picture in your mind where it sounds like the sound is coming from) and if you notice a loss in quality consider a better AMP (again why I suggested for $1000+ headset to get a used higher quality iFi at a lower price)
To recap
Your player, computer or phone or music player outputs a digital signal generally digital is all the same but the output quality generally matters up to "24 bit 96000 hz" consider this the minimum you want for headphones of your caliber ----> then the DAC turns this into Analog because of the complexity of this process the DAC cannot "add" (true fidelity)quality it can only lose quality, a "better" DAC will lose less quality and sound better... SUBJECTIVELY although usually very MINOR a DAC can add sound characteristics like warm or bright or OBJECTIVELY and NOTIBLY a DAC may do very good job not loosing aspects of the sound like detail or resolution(so if someone says a DAC is detailed or resolving the DAC is not making that happen it is making the loss of those qualities not happen) ----> a similar interaction happens with the AMP, an AMP cannot add detail or resolution (real fidelity) instead if an AMP is "detailed" or "resolving" it is because (first if it is, there is no weak point in the chain so whatever DAC it was tested with as the first part of the chain was good enough to let the detail or resolution not be adulterated) it is NOT destroying these qualities, a (usually) cheaper or "worse" AMP will lose these qualities... Same as a DAC to a slightly more extent and AMP may SUBJECTIVELY introduce qualities you make like such as warmth or brightness
So as you can see it is very much like a flow of a river of quality and introducing a sub-par component into this stream will cap the maximum flow of quality music and vs someone with the same pair of headphone and higher quality components, you will not be getting the maximum or closer to the maximum performance of a very expensive headset.... so budgeting is very important the same way as buying a gaming PC you should not blow the whole wad on the Graphics Card and have a bad CPU and bad RAM or you will never get the potential performance you paid for and generally have a bad experience....
The really important question is how much difference will these components make?
This is why I keep bringing up the iFi's... if you spend $200-300 on a desktop AMP the difference to a$500-$600 AMP will be very small because of the size.... good components can be had for around $200 but they are big and not great or sometimes not possible to use in a smaller portable AMP...
I know because I own a $170 MSRP Fiio A5.... portable AMPs are completely different... if you splurged and got a used Fiio E12/A5... you could get a used one under $80 on ebay even then I would say the difference is not terrible but it is noticeable maybe a %10-15 loss in quality for some on my higher end headphones vs a ~$200 desktop AMP where the $200-300 to $500-600 desktop AMP difference is maybe half or %5-10
So going from a Portable AMP from a Desktop AMP that cost the same price (Fiio A5 $170 MSRP vs Zen CAN $170 MSRP) There is a general %10-15 loss in quality that can be heard(detail and resolution) in a sense of when I listen on the A5 a expensive good headphone sounds good but as soon as I am on the Zen CAN it sounds noticeably better basically instantly for $500 pairs of headphones
This is droning on so let's get to the meat, the Toppin NX3 is likely built for much cheaper headphones ->
So here is what I suggest you do, try your headphones with just the DAC which is probably quite good for making sure you get the best audio quality and seems like a quality DAC with good reviews made for a Desktop setup and for a higher quality AMP
If you do not need more volume or want more bass then do not buy the Topping NX3
If you need more volume buy the Topping NX3 and carefully test it within the return period time to see if there is a notable difference in sound quality to you or a loss of enjoyment
If you notice a loss in sound quality and you lose enjoyment from that loss return the NX3 and look for a portable AMP with better performance or consider a larger semi-desktop sized AMP with portable capabilities as they generally perform better for what you pay(buy used under MSRP)
