Low gain dac!

Isn't 4.3V out on RCA from the dac against the normal specs/standards?

I thought they were supposed to be 2V on single ended outputs and 4V on balanced.

Yes the Redbook standard was 2v back in the 80's but since 2000 it's crept up now and the norm is 3v or more, which is good, as the higher the source voltage, the less end noise/hum/distortion there is because of less amplification needed down the line.

Nelson Pass,
"We’ve got lots of gain in our electronics. More gain than some of us need or want. At least 10 db more.
Think of it this way: If you are running your volume control down around 9 o’clock, you are actually throwing away signal level so that a subsequent gain stage can make it back up.
Routinely DIYers opt to make themselves a “passive preamp” - just an input selector and a volume control.
What could be better? Hardly any noise or distortion added by these simple passive parts. No feedback, no worrying about what type of capacitors – just musical perfection.
And yet there are guys out there who don’t care for the result. “It sucks the life out of the music”, is a commonly heard refrain (really - I’m being serious here!). Maybe they are reacting psychologically to the need to turn the volume control up compared to an active preamp."

Cheers George

If you want to keep all of your gear, then try reducing the signal level between your DAC and preamp by using an autoformer with a fixed attenuation.  Technically speaking (and in practice), an autoformer will sound much better than reducing the signal level by means of any type of resistive attenuation.  In fact, it may actually improve the sound overall (making it more detailed and dynamic).

Contact Dave Slagle.  For $200, you can pick up a pair of AVC (autoformers) and have them wired for any fixed reduction you would like (let's say about -10dB to -15dB might be useful for your case).  If you are feeling ambitious, you can get these transformers wound with silver wire at a cost.  I believe the transformers are about 1.5" tall, 2.5" wide, and just over an 1" deep.  You will need a pair of these to fit.  If you're not experienced, have someone who is help you out with this DIY.  Ideally, you can get these to fit within your preamp chassis and wire up directly.  Otherwise, maybe you can fit them within your DAC's chassis.  If not, then this solution probably won't be convenient.  Good luck.

http://www.intactaudio.com/atten.html

Buy a Chord Qutest, it has three selectable output levels. 1v, 2v, 3v

That is a nice feature on the Qutest.  

Yes agree, all dacs with digital domain volume should have this selectable output max voltage feature, then there’s no risk of "bit stripping" at all when using it direct if the volume is too low (<70%).

Wadia I think did it first with 6 x different levels on their top line dacs https://ibb.co/30WXsC1 but with user adjustable links inside. But if this option isn't there with a dac, then same can be done using a $49 Schiit Sys as max preset between dac and poweramp. 

Cheers George