What is the best sounding Mahler symphony cycle?

If you like Bernstein, "Mahler: The Complete Symphonies" box set has Lenny and the NYP at their best. It contains performances from the 1960s and has the most amazing remastering of any classical CD I've ever heard.
(DSD-remastered, 2008).

For a single 5th with good sound, try Abbado/Berlin Philharmonic (1993)

Brownsfan and I really like our classical; just want to clarify one thing. The Bernstein box set is a technical achievement in remastering, but not audiofile. But the old style of mic'ing and mixing the orch and great sonics makes it more pleasurable to listen to than many modern recordings.
The Lenny/VPO is early digital with terrific sound. The soundstage is very open with lots of detail. I say both are worthwhile.

Schubert...BIS is very mysterious; their website says that Naxos is their distributor. Have you ever made a purchase?

A definitive answer to the OP's question of audiophile quality is any of Zander's Mahler releases on Telarc. Although, I wouldn't consider Zander a top Mahlerian conductor, the Redbook CDs sound superb.

thanks Schubert. I guess I'll have to use Google and Naxos. (BIS has a catalog).

I really enjoyed listening to the 
Tennstedt/LPO on Qobuz. It's a very limited selection, so I think I'll go for the cycle that's available on Amazon.

@schubert , I'm listening to the Fisher via Qobuz. Really an excellent reading of Mahler. And the sound is outstanding; very well mic'd with ambience of the hall. 
Thanks for the recommendation. Possibly the best I've heard in years.

@mayoradamwest , @schubert 
The Fisher/Mahler are certainly audiophile quality recordings, and maybe that's one of the reasons for my enthusiastic response to them. I do think Fisher has a good grasp of Mahler from what I've heard. But since there's no compilation of the cycle, I'm exploring the symphonies one at a time.
It's a joy hearing symphonic music recorded with great care using proper microphone placement.

I think it's Grammaphone who lists the Budapest as a world class orchestra, currently rated at number 9.

To add to other's comments, I agree that Haitink/Chicago is top-class Mahler.

I very much like Boulez’s Mahler interpretations. I find them more intimate and less grand than my favorite conductors; eg, Bernstein, Abbado. It's a different take on Mahler.
The VPO recordings have the best SQ in the cycle probably due to the sonics of the wonderful Musikveiren and the recording techniques used.
Not quite audiophile, but worth having a listen.

I'll add to my previous comments that the Boulez  recordings are among the best in sound quality I have heard from DG. 

Has Mariss Jansons with the RCO been mentioned? I’m listening to the #2 live recording and the sonics are excellent. Not the most powerful rendition, but every detail by the Concertgebouw is heard with no harshness and with plenty of air and space defining the soundstage. The instruments and venue are well mic’d and provide 3 dimensional sound.
In hires it’s a most enjoyable experience.

@mahler123, I agree with your impression. He’s not much of a Mahlerian. It sounds restrained and never really peaks.
I’ve been listening on Qobuz, most recently #6 which I would call dull.
Superior quality recordings on the RCO label. I need to have a listen to other recordings in their catalogue.