Looks for Headphone Tube Amp

Yeah, don’t thank me til you’ve heard everything hooked up and run in a bit.  Realized I forgot to include interconnects — I think 0.5m Cullen Cable Copper Series RCA for $85 should work very well and hopefully not break the bank.  Look forward to hearing your impressions. 

No prob whatsoever. I’m just hoping this all works out well as everyone’s tastes are unique.

Anyway, you’re probably gonna hate me for this, but to me cables matter like tires matter on a sports car — underspend and you can ruin the whole experience, so what’s the point? That said, if I’m you I get an Apple USB 3 adaptor ($30) and either an AudioQuest Cinnamon ($80) or DH Labs ($70) USB cable. And, to make it worse, I’d also strongly consider getting an iFi Purifier3 ($129) to insert between your computer and DAC because computers are very noisy sources for music and will degrade your listening experience. You can always return it if I’m a liar.

The only thing I’m not sure about is the USB 3 adaptor for the MacBook because I don’t use a MacBook, but you need a way to get from the Thunderbolt/Lightning port to USB and this is the only thing I know that does it unless there’s another/better option. Anyway, that’s my rabbit hole if you choose to jump in.

USB from computer to E30 should work fine.  The Toppings will probably require some hours of playtime to break in and sound their best so try not to judge too quickly.  Let us know what you think. 

Looking closer at your headphones I’m not sure the iFi would be the best match sonically nor would a tube amp given the 99’s low input impedance.  Personally I’d be looking to a more neutrally-voiced amp/DAC like the AQ Dragonfly Red that I own so know its sonic signature well, and the Stereophile reviewer who reviewed your ‘phones also used the Red and it seemed to work well with them so you might want to read the review.  What might be an even better option for another $100 if you don’t need portability would be the Topping E30 DAC and L30 amp separates.  Anyway, just some further thoughts FWIW. 

should I use both a DAC and an amp?

Absolutely — your headphones are plenty good enough to reward you significantly by feeding it a better signal, and the DACs in iPhones and iMacs suck and will greatly limit your sound quality. At your budget I’d avoid tubes and go with a combo amp/DAC like an AudioQuest Dragonfly Red or something from Topping, etc. And get Qobuz instead of Tidal if you can — it’s cheaper and better with none of the intrusive MQA crap to deal with. BTW, you’ll also need an Apple Lightening to USB 3 cable (about $30) to be able to bypass the device’s internal DAC.  You won’t hear much difference with crap MP3 tracks, but CD resolution and up will sound much better.  Hope this helps, and best of luck.

What DAC are you using and what is your music source — ripped CDs, Qobuz, etc.?