Jeff Evans
So you need a balanced XLR to TRS cable to get the signal in.

 
Why not just use an XLR to XLR cable ?  That's what I'd do.  Why the conversion ?
The Presonus Tubepre has an XLR output (balanced).  Its 1/4" output is not balanced (only TS).
 
Here's a schematic for another Steinberg product that shows a similar input circuit where XLR and TRS are just wired together (you can ignore the Hi-Z switch).

Paul P

Jeff Evans
So you need a balanced XLR to TRS cable to get the signal in.

 
Why not just use an XLR to XLR cable ?  That's what I'd do.  Why the conversion ?
The Presonus Tubepre has an XLR output (balanced).  Its 1/4" output is not balanced (only TS).
 
Here's a schematic for another Steinberg product that shows a similar input circuit where XLR and TRS are just wired together (you can ignore the Hi-Z switch).

 
Well, I just ran some tests.  I kept the gain on the audio interface completely down and had the gain on the preamp up at around 50%.

First I tested XLR -> XLR, then I tested using the XLR -> TRS cable to the audio interface.  The XLR connection was about 15db louder than the XLR -> TRS connection (no changes on the gains made).  This proves the XLR connection is adding amplification.
 
I bought this cable for my XLR -> TRS connection:   http://www.amazon.com/gp/product/B00OWG4MV6?psc=1&redirect=true&ref_=oh_aui_detailpage_o02_s00
 
Am I ok with this?

Thanks everyone for helping me out, I really appreciate it.  I'm sorry I don't understand all of it.

SilverBlueMedallion
The XLR connection was about 15db louder than the XLR -> TRS connection (no changes on the gains made).

 
Glad you've worked things out.  I just read the manual and as mettelus pointed out, and you've been affirming, there is a difference between the two.  This is not always the case.
 
"When connected to an XLR-type plug, this jack automatically switches to microphone input sensitivity, and when connected to a phone-type plug, it switches to line input sensitivity."
 
You should be fine with your cable.

On the block diagram it says
 
Mic Input Nominal level -54 dBu to -10 dBu
Line Input Nominal level -34 dBu to +14 dBu
 
Specs say Max input level for Mic is 0 dBu
               Max input level for Line is +24 dBu
 
That tells us the attenuator is reducing the gain by 24 dB from Mic to Line level.
 
Hence reason why XLR to XLR is not a great choice.  It would work but you may overload Mic Pre
XLR to TRS is great choice so now you have 24 dB of headroom.  Presonus Pre will never overload it then.
 
Also Input impedance is only 4K ohm on the XLR which is OK but lower than 20K on line input.  The fact the Presonus output impedance is very low eg 50 ohms means it will still drive into a 4K ohm load fine. (so will a microphone because Mic output impedance is usuall pretty low)
 
If the output impedance of the Presonus was say 2K ohms then things would be different. 2K feeding into 4K means signal loss. 2K feeding 20K however would not be significant if at all.
 
Rarely are XLR and TRS wired directly in parallel if feeding the same Mic Pre although I have seen it. Usually there is some form of attenuation going on from XLR to the TRS jacks.
 
Capacitors usually block any phantom power as well from getting back into the line inputs. (from the XLR's) Although that is worth checking. The diagram does not show any but they should be there.  If you feed a Kurzweil synth (latest models) into XLR/line inputs that have phantom power present you will blow the output stages of the Kurzweil in an instant. (they told me so!) I nearly fed mine into a pair of XLR's that had phantom power on them but decided to ask them first. Just as well I did!
 
Phantom power would not harm the Presonus Pre because usually valve pres's have an output transformer that would prevent that DC from doing any harm.
 
Sorry, just some useless information.

no no, not useless... good stuff in there - i don't understand electronics really, but you made me feel more confident in my XLR > TRS cable :)
 
Thank you!

Jeff Evans
 
 
You are probably better off running your Mic signals direct to the UR22 unless of course the sound of the Presonus Valve Pre V2 is really offering something that you want of course.  There are plugins out there that can emulate the sound a valve Pre as well you know. 

I use the UR44 (guessing the same pres as the UR22) and the mic pres on it do not offer enough gain for many mics.  Hence I use an outboard preamp as well, before going into it, so the gain on the Steinberg unit isn't cranked to max.  With little gain on the initial preamp and the same on the Steinberg, things are kept pretty quiet.  But for typical ribbons and even my dynamic RE-20, the Steinberg doesn't cut it by itself.  Besides the low headphone volume the unit also produces, I'm liking it...but two major downfalls imo.

I've never had a problem using XLR- balanced 1/4 inch.  I've had to buy a few for using outboard.  Some times they do make it hard to tell, esp. on the internet, but balanced to balanced (I've never seen an unbalanced XLR but that doesn't mean it doesn't exist, esp. after running a dolly over it a few times).
 
XLR from preamp output to 1/4 inch line input on a combo input should work fine.  As detailed above, most automatic switch sensing basically pads the line input as it goes to the mic input.  Plugging an XLR line output into an XLR mic input will drop your beautiful line level signal way down into the noise.
 
FYI, I've used many Monoprice cables available on Amazon with few problems and no returns (yet!).

The UR44 is slightly more interesting interface. The Mic Pres do look similar but the UR44 in fact has a dedicated pair of proper line inputs. eg channels 5/6. These inputs have no actual Mic Pre as such. They are balanced inputs and accept a much higher level and have a higher maximum input level as to be expected.
 
So if you a running a full Mic Pre prior to the UR44 you should be patching the output of your Mic Pre into inputs 5/6 instead and avoid the Mic Pre inputs all together.
 
Unless as mixmkr points out you may want to run a mic into a Mic Pre and use a little less gain there and then out of that into a Mic Input on the UR44 and use a little more gain there which you could do for sure. You will get more gain that way overall.  Maybe a little more noise at the same time but it may not be too noticeable.