Disclaimer: I took the advertising photography for the Noble Audio BTS. Noble Audio sent me a BTS several weeks ago, at no cost to me. BTS MSRP is 99$ USD. You can find more about it here.
Not all bluetooth implementations are created equal. Few, if any, are capable of bumping the theoretical limits of 16-bit audio. Then there's compression: AAC or SBC. Apt-X solves some of the issues, but isn't all there yet. (The Headphone List's article on each is worth a read.)
As a matter of course, current Bluetooth audio simply isn't up to the noise/dynamic range/crosstalk/distortion and so on, requirements of 24-bit audio. Still, Noble Audio's BTS syncs, and plays back both 16-bit 44kHz and 24-bit 44kHz files, sans problem.
How well it plays back 16-bit audio depends on the device feeding it. After pitching an iPhone 6 an iPod nano 7 and a MZAK100 (Astell & Kern AK100 mod) against each other in various hardware tests, it is apparent to me that the MZAK100 is the best source for the BTS. Its lead over the iPhone 6 is small, but measurable. Its lead over the iPod nano 7 is cavernous, and audible.
By ear, differences between the iPhone 7 and the MZAK100's bluetooth signals come down to output volume levels, the MZAK100 kicking out a signal loud enough to clip the BTS's output. Volume-matched and blind tested, the BTS is mostly agnostic.
Its background noise is equal irrespective the source, and is slightly higher than the stock AK100, or slightly lower than a 2005 iPod nano, which makes it suitable for most earphones. Channel balance is precise, and volume can be adjusted both from the source, and via the BTS volume buttons.
BTS gets loud enough to power the DT880/600 in my drinking room. But Chase Emory would probably want more (volume, not scotch). As would Charles Wong (both). In fact, I've clicked the BTS's volume minus button twice since taking my first sip.
The only metric in which the BTS performs below par is crosstalk, but even at 47-49dB, it bests a small number of standalone portable amplifiers I have tested. It returns very good to excellent results for dynamic range and noise, good results for THD, and when fed signal through a well-implemented bluetooth transmitter, good IMD + Noise results. Most of its results are light years ahead of the PS Audio Sprout's (in Bluetooth).
But if you want it to perform its best, you'll need the best Bluetooth signal possible. Fortunately, the iPhone performs well. But there are other, better, options. The 2,5 year old AK100 is one. If and when other Bluetooth sources cross my desk, I will add them to the results below.
NOTE: the below unloaded results exist to show the differences in Bluetooth signal quality between sources when feeding the Noble BTS.
The following are the results of Rightmark Audio Analyzer tests for the Noble Audio BTS.
Source 1: iPod nano 7G
Source 2: iPhone 6
Source 3: Mezzo Hifi MZAK100
ADC: Lynx Studio HILO LT-TB
Computer: 2012 27" iMac
Cables: 1,5m Hosa Pro 3,5mm stereo to dual 3-pin XLR (around 8$)
NL - no load
SM2 - Earsonics SM2
ES7 - Audio Technica ES7
DT880 - Beyerdynamic DT880/600
First, 16bit 44kHz RMAA comparative results:
Second, 24bit 44kHz RMAA comparative results: