Do I need an external DAC to play my music files?

I currently own an Integra DHC-80.1 and an Oppo BDP-95. I usually plug my usb stick into the Integra to listen to my files. Am I getting the most out of my system in doing so (not the most techy person)? I read somewhere that even if it is reading at 44.1kHz it is not the best. What would solve this?
I'm a little unclear about what you are saying. I know that the Oppo is a nice sounding unit, but are you saying that you are using the internal DAC in the Integra unit to decode your music files?

If this is what you're saying, I think that you can do better than the internal DAC in the Integra. Digital to Analogue conversion is one area where choices are vast....VAST.

No matter what your Integra sounds like, you can probably do better, if you spend enough money. How much money depends on how good your present DAC is.

If the DAC in the Integra is like any other DAC in an all in one home theater unit, it probably won't be hard to better it for under $1K. Maybe a lot less than $1K.

What's the problem with what you're hearing now? Or are you just exploring this because someone said that you can do better? If you have no complaints, I wouldn't worry about it. On the other hand, you never know what you're missing until you've heard better.
Both DACs (integra and oppo) feature 192/32 bit...I was just curious if I was missing out by using either of these to play my music files.
What resolution your DAC plays back in depends on the file structure and resolution of your music files. If you have ripped a standard CD, they will most likely be 44.1K/16 bit. Some DACs will "upsample" this resolution to higher bit rates, and some find this upsampling to be a detriment rather than an advantage. So playback at the native 44.1/16 is not always a bad thing.

Other high resolution music files are available from download sources or commercially (like the Apple Beatles release) and this music is in a higher resolution format. Higher resolution files are probably never "downsampled" to 44.1/16, but are played back at their native resolution.

So it all depends on your files and whether the Integra automatically upsamples them or not.
If you took the USB stick and plugged it into the Oppo and then connected the Oppo to your preamp using analog cables, you would be using the Oppo's DACs, which are quite good...

When I play my music files on the Integra, the song is displayed at whatever the bit rate (192/256/320,etc) and then 44.1kHz. And I've read that there are DACs that take those files and boosts them from 44.1 to 192. So what is out there that does this (relatively cheap) and/or is this even worth the trouble?
I believe that Kal (Kr4) has reviewed the Integra and I know he has experience with the Oppo. Maybe he'll jump in with some advice on the relative merits of their DACs and how the upsampling on each works.