Using external DAC with preamp with built-in DAC

Yes, Barnabas. It will work.

Yes, using the built in DAC is optional. 

If you like the sound of the DAC you are using, you may be better off buying a preamplifier that focuses only on the analog circuit. You could bypass the other built in DAC but it seems counterintuitive and increases the risk of noise. 

Yeah, if you’re gonna use an external DAC you’re better off just getting an analog preamp without a DAC to avoid the added cost of something you likely won’t use and noise.  As others mentioned you can use a pre with an internal DAC no problem, but check to see that it doesn’t digitize all inputs because you don’t want that. 

Most high quality preamps do not have an internal DAC. I Don't recommend them, even if there is a slot. In general, you will get better sound by isolating functions. So, a preamp only being a preamp. Depending on your budget I'd looks a used Conrad Johnson, Audio Research or VAC preamps. These and other high end companies may outstanding preamps that will last for decades. 

Without knowing what make/models you have been looking at, I would caution you to not confuse an external DAC and/or streamer that also can operate as a preamp (i.e. has a volume control) with a true preamp.  Typically their focus is on the digital side and do not sound as nice.  An example of this would be a Cambridge Audio CXNxxx series as aposed to a Hegel H120 or PS Audio Stellar Gain Cell, which have an analog preamp section and the DAC is an "addon". 

Absolutely yes.

Yes, you can use it through an analog input as others have said. But absolutely plus one on a pure preamp will sound better!   I don’t know your price range, but an Audionet Pre G2 was my first ear opening foray into amazing sound.
 

@OP - I suspect you are looking at preamps at the more affordable end of the market as it's those that tend to have built in DACs.

The majority of high end preamps are analogue only.

Of course it will work.  But try it both ways to see what you like best.

I hooked up my old Arcam DAC to the line in's and did an A/B against the resident DAC in my integrated. The resident DAC in the integrated uses a lower end ESS chip compared to the TI chip in the Arcam, but the Arcam DAC is close to 15 years old. The lower end but newer ESS chip sounded better to me.. 

I just got a Quad 33 all analog preamp, using an outboard SMSL DO200 Pro DAC with it. The signal path is all balanced XLR. The Quad has MM/ MC phono, a good headphone amp, and useful tone controls, for well under $2K. I had a C-J PF-R before this, and I like this better. 

@yoyoyaya - Yes, I am looking at more affordable preamps.

Thanks everyone for your comments and suggestions!

Have 2 Benchmark LA-4 pre amps. NO DAC inside,  Using both balanced. Made in NY, 30day trial I believe, remote extra. Around 3k each, definitely priced very fairly. Rory,  who will answer the phone is very knowledgeable!  If you try it, You will keep it!