why a high end phono preamp?

I recently purchased a Hegel 160 integrated amp with no phono stage.  I also purchased a NAD c 427 tuner, and have a Dual CS 5000 TT (I have no idea what type of stylus it uses).

I wish to play my vinyl's but don't understand why I can't do with a $49 phono amp as opposed to one that costs hundreds of dollars. 

Is it the Hegel that is responsible for delivering superior sound, or is it the preamp? I thought the cheaper item is solely a conduit for the power, but is it the product that allows the record to be heard properly? Any recommendations for my components? I was looking at Clearaudio Nano V2. Thank you.
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Phono preamps can sound very different. Aside from the accuracy of the RIAA curve applied (or support for other curves), the sound character can vary widely. I would say it quite easy to find phono preamps that sound very different from each other.

A phono preamp is performing frequency response adjustments, and also has an amplification stage. Plus it has a direct and significant interaction with the electrical properties of the cartridge, tonearm, and phono cable. So in some sense it is more complicated, and sensitive, than an integrated amplifier.
A quality phono preamp makes a huge difference.  I didn't hear vinyl for what it could be until I got a great one.  I don't think you have to spend a fortune but it is a necessity if you want great sounding vinyl.  

I think a lot of folks get into vinyl and abandon it prematurely because their phono preamps are not that good, giving them dry and plain sound.  

Michael Fremer loves this one at about $550.  https://www.musicdirect.com/customer-favorites-our-best-selling-gear/ifi-micro-iphono-2-mmmc-phono-p...

About 3 years ago, I was on here asking for help identifying my weakest link in my system.  I got advice all over the place.  One guy told me a better phono preamp would take me to a better level.  He was spot on.  

In some ways, I think a phono preamp seems like an un-sexy purchase in this hobby.  Once I made the leap, it was the best thing I've done.  
I upgraded my phono stage in the past year replacing a 25+ year old unit.  At first, I tried a sub $1000 unit made by a well respected phono preamp designer.  Giving it weeks to burn-in, I could only conclude that my cherished vinyl was being ill served.  So...after absorbing a modest financial hit, I traded in that new phono stage for a significantly more accomplished unit.  Night and frickin'day!  Besides a new life breathed into my vinyl, the shocker was how LP surface noise was minimized by the upgraded unit as it navigated those unmusical noises more adroitly.  In short, at least in my experience, investing in a fine phono amp is well worth it.  
I'm sure someone more technical can explain this better but a phono preamp is taking a very small signal and magnifying it many times and also applying a riaa equalization to the signal. No small feat and how well it is done is definitely going to affect sound quality.

You don't have to spend a fortune for an outboard phono stage, the new Parks Puffin punches well above its weight at $400. My $1000 phone stage is for sale now after getting the Puffin.
+1 jbhiller " A quality phono preamp makes a huge difference"
IME, this is absolutely true. I've used preamps that were stated to have excellent phono sections (melos & Jeff Rowland) & didn't get the sound quality I was looking for until I went with a dedicated phono preamp. The first one was a sonic frontiers signature phono amp. The second is Audio Alchemy's latest with optional power supply. Big difference.
"Is it the Hegel that is responsible for delivering superior sound, or is it the preamp?"   Everything, from the quality of your vinyls, to your speakers/room acoustics, is responsible for superior sound.   A chain is only as strong as it's weakest link.  
With the best amps and speakers, you can't make up for a loss upstream. A good phono section is mandatory for good vinyl playback!
For a budget of $500-$600, I’d recommend either the Lehman Original Black Cube or the ifi unit mentioned above. If you’re on an even tighter budget, you can try the Schiit Mani but you should splurge for a linear power supply if you go that route. A good/decent phono preamp does make a difference but it should be within reason given the turntable/cartridge sitting behind it. I think your planned budget is within reason. 
You might be just fine with that 49 dollar phono stage if you don’t have a good stylus it’s all down hill from there in the chain.     
Op, I hope you don't mind if I ask perhaps a related question here.  Are all stand along phono preamps both MC and MM?  If a person knew they were only going to be using MM can a MM preamp only be purchased, perhaps even at a price that reflects it not having the not necessary MC electronics?
Yes you can purchase just a MM phono preamp Soundsmith for one makes them, I'm sure that there are also many others available.
Are all stand along phono preamps both MC and MM? If a person knew they were only going to be using MM can a MM preamp only be purchased, perhaps even at a price that reflects it not having the not necessary MC electronics?
Most inexpensive phono sections are MM only. You need more gain and a good noise floor for LOMC cartridges- and that costs more.
One other thing about a good phono stage. A good one will exhibit less ticks and pops due to better RFI resistance and good overload margins.
Are all stand alone phono preamps both MC and MM?

There is a school of thought that designing a lower gain MM only phono stage is optimal and using transformers to deal with the additional gain of an MC cartridge. Given the diversity in characteristics of MCs (both output and loading needs) manufacturers often elect to leave the selection of transformer up to the user.  Allied to this is a belief in keeping the phono stage as simple and option free as possible to focus on the purity of the amplification and equalization

That's at least the philosophy of the maker of my phono stage, which is a pretty high end model and I will say that for this end user at least it works well
OP, your suggested Clearaudio Nano V2 phono section looks good and proportionate to your other gear in terms of quality and expense. What are you contemplating for a phono cartridge and speakers?