The DAC built into your soundcard may be perfectly adequate. A headphone-output can double as a line-output. If you don't hear noise (hum, hiss or whine in the background) it's probably better than human hearing. The other important specs (noise and distortion) are almost always better than human hearing. (Once I had a soundcard that made noise when the hard drive was accessed.)
You may not need a preamp either. A preamp is mostly a "control center" with multiple inputs, a volume control, tone controls, etc. Sometimes a volume control knob, or remote control is nice if your DAC doesn't have an one. Tone controls are nice too. It's easier to make a quick tone control adjustment than to fuss-around with digital EQ.
Then I will go to preamp from rca outputs on dac? What do the other end of those rca cables go into on my preamp?
A traditional preamp has multiple line-inputs, sometimes labeled "CD", "tape" or "aux, maybe even "DAC". (A "phono" input is different.) A modern preamp may have digital inputs (and therefore a built-in DAC) but HDMI and S/PDIF (for DVD & Blu-Ray players) is more common than USB.
You didn't say where you're going from there... A power amp or active-powered speakers?
I'm not really an expert on streaming. I'm not sure if you can high-resolution lossless if you use Bluetooth. Even with wired USB connections, if everything isn't configured perfectly, high-resolution can get down-sampled to 48kHz or 44.1kHz. (You'll still get the bit-depth of your DAC, usually 24-bits.) But regular resolution "CD quality" or even lossy compression can be excellent and you might have to listen very carefully to hear a difference, if you can hear a difference at all. Sometimes the high-res version is mastered differently and then it can sound different... Hopefully better, but you can't always be sure...
Better (or different) speakers (or headphones) will make a bigger difference than switching back-and-forth between high resolution and standard resolution, or even good quality MP3! If you can get high-resolution that's great! But speakers (and room acoustics) are more important.