I didn’t realize that you were using the Hegel internal DAC. I assumed you were using the Buesound as DAC. That being said, it is still my opinion that an external DAC will do much better than the Hegel internal DAC. I wouldn’t mess around with upgrading the digital cable. In my experience, the cheap Blue Jeans "Belden 1694A" digital coax cable is extremely good. I have not tested super expensive digital coax cables, but this Belden has beat stuff up to the $150-200 level. Make sure you get a 6 foot cable (short cables are worse actually).
The Lumin D1 is an interesting device. I took a quick look. However, I think it has some things lacking. First, the power supply is basically a wall wart, and there doesn’t look to be any good power supply internally. Second is that it uses 49860 op amps for both I/V and output buffer. While the 49860 are okay, I think that using discrete circuits are much better. For $2,000, I would actually look elsewhere for a device.
http://www.stereolifemagazine.com/images/reviews/lumind1/w/LuminD1-03w.jpg
The Marantz NA8005 has a lot of internal power supply management (which is critical in my opinion), such as large transformer, much voltage regulators, large capacitance bank, etc. It also has discrete analog output circuits (though only has RCA outputs). It has many of the streaming audio functionality (apply airplay, DLNA, internet radio, etc., IOS/android control app, DSD support), so you could potentially replace your Blusound unless you require wireless network.
http://www.alpha-audio.nl/wordpress/wp-content/uploads/2014/12/Marantz-NA8005-intern-3.jpg
The Gustard X20 has fully discrete analog output circuits and also supports balanced XLR audio outputs, but it is only a DAC (not a network player), so you’ll still have to use your Blusound for streaming/playing. It is somewhat cheaper than the Marantz. May be a better power supply than the Marantz, but no network streaming/playing.
https://littlemart.files.wordpress.com/2015/08/x20d.jpg
Both are probably very nice choices in the $800-1200 area. I’m sure there may be other choices. With this cost, you could spend money on a couple of good power cables (for Hegel and new DAC) as well as a good interconnect (Maybe a Wire World, but there are many).