I have found that the DAC one chooses does make a substantial difference.

My past experience is this, the three cheap DACs (<$500) I've owned with op amps in the signal path

had sound output that was flawed. Specifically etched treble, compressed or artificially wide soundstage,

and lack of instrument separation. (congestion during complex sound passages with an orchestra, for example.)

I'm not a fan of DACs with tubes in them either due to the euphonic coloration they impart.

The addition of tubes does sound good, but doesn't render true sound reproduction.

This is called poor design implementation...NOT because of op-amps=see what you stated below-

I wont name names, I do not want to upset any "members of the trade" around here.

For the OP, it may be important for the person to know your opinion of specific devices that you recommend the OP to stay clear of.

I cannot say that I have owned any $1000+ DACs with opamps in them,

although I have listened to some at meets and they did sound really good.

Which confirms that it is all about the design, OR that better associated speakers were being used.

My current mid-fi setup consists of a DAC and an amp that do not utilize op amps or tubes and sounds superb.

FWIW, I do own a few cheap tube amps for when I am in the mood for a euphonic sound experience.

I can guarantee you that if you hear a properly designed device, regardless of what it is and what is being used in the design (op amps, tubes, you name it), that you would even be surprised at how tubed based devices actually can sound far far harsher and aweful vs. an SS device, and at the same time, that a tubed device can sound identical to an SS design when both are designed by a similar engineer and with properly implemented circuits that are tailored to sound transparent regardless of the fact that they use SS based components vs. tube based components.

I do agree with you that a poorly done DAC can sound really bad, but I do not agree that the system will lose much soundquality as long as the speakers being listened to are at the soundquality the listener enjoys most.  I know I have listened to many different devices and the only time I heard such a massive difference was when I put on the vinyl based digital equivalent:)

Cheers!

I'm not buying it. You can get a device that successfully converts a digital signal to an analog one for next to nothing, sure, in much the same way that a coat hanger can successfully act as a speaker wire. Sound comes out the other end. Doing that job well though means a good power supply, a low jitter receiver, a high quality DAC chip new or old and a well designed, high quality analog output stage. That stuff still costs money. While I'm not saying that you need to step up to the level of an MBL 1611F, I would advise that people spend at least a grand on their DAC if they want things done right.
 

Some things cost money to be done right, some don't. DAC's don't. 

This $30 DAC has a THD of .008%. That's a fraction of audible distortion @ .05%