Need to under stand Asynchronous USB

So I just got a Marantz ND 8006 Network CD player. Im using it as a network player and CD transport  and I output digital to my NAD M51 DAC. I’m using my IPad to stream TIDAL and that works tip top. However, it’s the USB inputs that concern me. I have a choice of a front connection and a rear USB DAC connection. 

Couple questions:

1. The USB DAC input is for a Mac or PC hook up, but is there any other way to use an input like this?  Does it have to come from a computer or can a USB hard drive work with an input like this?
2. More importantly the front USB input is NOT asynchronous.  I think they make a reclocker I can put in between the USB and the unit. My question is do they make a USB hard drive with a built in reclocker with a good amount of hard drive space?

this is all new to me, so any help would be appreciated. 
1) You can use a USB flash drive, iPod or other portable player.
2) Asynchronus is what you want. The DAC being fed by the input reclocks the data and this is the ideal.
Item 2) you mention, does that mean my DAC does the reclocking and I don’t need an external reclocker?
I have the M51. The USB - the type B - input is async from XMOS. The DAC uses its own clocks. However, it’s been widely agreed from reviews and users (and I concur, also) USB is not the best input for it rather than AES. I tried various USB decrappifiers from iFi and linear power supplies, as well as various coaxes but they didn’t swing that judgment.

I use a Yellowtec PUC2 Lite which is a USB-AES converter and that’s the best sound I get from the M51. Sound is muscular and detailed.

It seems to take a great deal of extraneous gear for USB to perform optimally (reclockers, isolators, power supplies, e.g. SOTM or Uptone kind of thing), by which point you could have gotten a better DAC period!

The other USB - type A - input you’re talking about implies using a USB flash drive for local playback. That’s not what the other USB jack is for - rather it’s for updating the firmware (1.39 is best for the M51 rev1!)

If you want to use a computer and/or network storage as a front-end, then you might want to look at a streamer (e.g. Bluesound, Auralic) with any kind of digital output. It can be USB, optical, coax, even HDMI, or AES, but as I said, the M51 likes AES the best. Or indeed track down a Yellowtec PUC2 lite + USB streamer.
Moto. I’m feeding the DAC info through the Marantz.

I guess im still a little confused. I’m runner no a standard thumb drive into the Marantz witch then sends it via coax digital out to the coax in of the DAC (nad m51).

Do I still need a reclocker or something?
Either USB input will have equivalent performance.

Asynchronous USB refers to the DAC being the conductor in the communication. The PC/Mac software or whatever doles out data as the DAC requests it. So, it’s a cooperative arrangement. The PC/Mac picks what to play, reads it and sends it down to the DAC, but the DAC remains in control of the metronome.

The front USB connection is for media devices, including a hard drive. Since the Marantz is also acting as the player software, the idea of asynchronous is kind of irrelevant.

In both cases the DAC will be in charge of the metronome.

Now, if you use S/PDIF via optical or coax this no longer happens. Then the source device owns the clock, and the DAC better keep up.

Oh I get you now, @last_lemming . The Marantz is feeding the contents of your USB drive via coax to the NAD. Like Erik said, for coax, the clock is embedded in the SPDIF data stream from the Marantz. Here the source is the clock master and this signal is synchronous. Folks used to sell SPDIF reclocking devices on the principle that the clocks in most original SPDIF sources (e.g. your Marantz) were bad (i.e. causing high jitter) and the doohickey reclocker would be better....

Now, you could stick the same files on a laptop and plug the laptop into the NAD’s USB input, but this time it’s async cause the DAC controls the clock. Despite this improvement, folks still try to improve the quality of USB sources with new doohickeys (that I mentioned in previous post) on the basis that computers have a lot of electrical noise that come into the DAC.

This is an old article from wavelength but still explains the concept of async USB

You can also read product briefs on things like the iFi iUSB3, Uptone USB Regen. Folks have also now moved to Network sources and transmission devices like your Marantz all-in-one, Auralic G1, SotM, DCS Network Bridge, etc.

I don’t think you need a relocker in either case cause of pitiful diminishing returns! Expect strong rebuttals from those hawking the doohickeys! Note I’m not saying none of these devices can improve the sound, I’m saying they’re usually expensive to the point of (all added up) where you could get a much better DAC / room treatment / Scotch / beer money.
Last follow up, trying to improve the USB stick input on the Marantz would be sketchy. It’s going to be one of those USB 1.0 devices like on a cheap blu-ray player, and you’re still connecting to the M51 via coax anyways.

I mean, you’re using the Marantz as a pass-through atm (effectively you’re using it as SPDIF output), for which I see no real benefit apart from when its playing CDs (which you could rip and either play directly to the NAD or stream via the Marantz).

I see the 8006 has ethernet and wifi inputs and USB output, so on paper, the best layout would be:
1. files on network storage (computer / laptop / big USB drive / NAS)
2. ethernet or wifi to Marantz
3. Marantz USB out to M51 USB in -- here is where you may want to try a USB reclocking doohickey OR
3.1 Marantz USB out to M51 AES in (like my Yellowtec PUC2 Lite / Berkeley Alpha USB, e.g. USB-SPDIF/AES converter) OR
4. Marantz SPDIF out to M51 SPDIF in -- there are still some SPDIF reclocking doohickeys

Where this could get very silly is a config like (just picking products at random)
Marantz USB out > Uptone Audio USB Regen > Yellowtec PUC2 Lite > M51 AES in --we’ve all tried this kind of thing, though! It’s probably why a lot of manufacturers have more and more all-in-one network players like your Marantz, or separate network transports, even combo network streamer-DAC-preamps. So many damned cables and power supplies. And DC umbilicals and power cables to sell for them!
How much quality is lost streaming Tidal via wireless vs hardwired?  I read that wireless is not so good. 
It depends on the device. The old squeezebox touch's digital out was better wired vs wifi, but times have moved on, e.g. with the new Auralic stuff, wifi is reported to be equal if not preferred. You can just try comparing the two on your Marantz.
So I use tidal through my iPad to control the Marantz streaming. The Marantz is connected to my WiFi, so is the actual music data coming from my iPad or my computer in my room where the WiFi is located even though I have no app downloaded on my computer ?
...the Marantz is doing the playback; the iPad is just a remote control; your wifi network contains all the data being sent to and from the Tidal servers