Bluetooth is a popular way to connect devices wireless. Mouse, keyboard and other peripherals, when connected wireless it is by Bluetooth.
In audio Bluetooth is often used to connect a player and a headset wireless.

Often this is done by plugging a Bluetooth dongle in the headphone out of the player.

In this case, the audio is converted from analogue to digital, send to the receiver and converted to analogue again. Not exactly an audiophile's paradise.

A2DP

Best audio quality is obtained using the A2DP protocol.

It supports the following Codecs:

SBC (sub-band codec) is mandatory.

This profile limits the available maximum bit rate to 320kb/s for mono, and 512kb/s for two-channel.
MPEG-1,2 Audio
MPEG-2,4 AAC
ATRAC (Sony)
In essence high bit rate MP3 but vendors can implement their own protocols.

With a nominal bandwidth of 3 Mbit/s (2.1 + EDR) it is not really suit for high resolution audio.

APT-X

A proprietary codec by CSR
As it is not a mandatory part of the standard you need both a sender and a receiver supporting this protocol.

It is a lossy protocol but said to improve sound quality wise on SBC

• Compression ratio: 4:1
• Word depth: 16, 20 or 24-bit audio supported
• Data rates: 60 kbps to 576kbps (16-bit 15 kHz mono to 24-bit 48 kHz stereo)
• Frequency response: 10Hz to 24kHz
• Delay: <1.89ms @ Fs 48KHz
• Dynamic range: 16-bit>92dB, 20-bit>112dB, 24-bit>120dB
• THD+N: -81.1dB (0.008%) (24-bit)
• Sample frequencies: 0-48kHz
• Auxiliary data: Embedded, sample rate dependent up to 1/4 Fs kbps
• AutoSync: Can re-establish connection in 5ms
• Bit error resilience: Up to 1:10,000

If you want CD quality (16 bits/44.1 kHz) you might have a look at wireless systems using KLEER or SKAA.

Sleek SA6 and Wireless W-1

SA6 can be used wired too

Hardware

Artora amp with up to 16 Bluetooth inputs.

1. Bluetooth SIG
2. Optimally Using the Bluetooth Subband Codec - Christian Hoene and Mansoor Hyder
3. APT-X - CSR
4. APT-X - Wikipedia
5. APT-X - Hydrogenaudio
6. KleerNet™ - Smart Mixed-Signal Connectivity