Headphones

To my knowledge, you don't use wifi the way you think. You only use Bluetooth. What I can think of is buy a short cable that fits the Meze 99's. Ali express has short cables at .5 meters. Then buy multiple Qudelix 5k's to hook up to the short cable and there's your hotswap capability. Or you can use the regular cable and put the Qudelix in your pocket. For longer battery life you can get something like the ifi xcan. Or maybe you're really good at diy and can do something with a tiny version of raspberry pi. Then you plug into that and then you would get wifi going to the raspberry pi.

You don't need to mod anything. Just buy a BTR5, BTR15, Qudelix or one of the other Bluetooth DAC/amps. They have internal batteries that last a long time. The 99s are easy to drive so any of them will work, but a balanced cable should make it sound better. You don't need one for the Meze though.

Any of the Bluetooth amps can connect wired or wirelessly. They can handle LDAC if you want lossless.

Try Qudelix 5K or any Bluetooth amp/DAC dongle.

Qudelix 5K and other dongle info: https://www.reddit.com/r/HeadphoneAdvice/comments/17zjxp6/looking_for_desktop_dacamp_gaming_budget_250_aud/k9zw9b6/ and https://www.reddit.com/r/HeadphoneAdvice/comments/13a1rdm/noisy_amp_in_new_apartment/jj4y67a/ and https://www.reddit.com/r/HeadphoneAdvice/comments/136sxe8/qudelix_5k_vs_khadas_tea_vs_btr7_with_iphone_and/jir8k23/

Or FiiO UTWS5 + adapters/converters for your Meze 99 Classics/particular headphones plug + KB9P AptX Adaptive USB transmitter dongle. If you're using iPhone/Apple/etc. make sure to get an OTG (allows data transfer) adapter/converter for the KB9P/etc.

See here for more info on how to use the UTWS3/5 with headphones instead of just IEMs: https://www.reddit.com/r/headphones/comments/109gr1t/here_is_the_follow_up_post_of_the_hd_660s/j3yngj0/?context=10000 and https://www.reddit.com/r/headphones/comments/109gr1t/here_is_the_follow_up_post_of_the_hd_660s/j3yq4vs/ and https://www.reddit.com/r/headphones/comments/1095ijp/i_made_a_pair_of_bluetooth_adapters_for/j408j33/

There's also the LC3 and AptX Lossless transmitters/dongles available now from Creative Labs (check their newer headphones, TWS/Bluetooth stuff)/random Kickstarter projects/but unfortunately they're like double or way more expensive than the ~$15 KB9P dongle.

And at the moment, there's essentially no LC3/AptX Lossless/etc. TWS adapter yet. Like there's the QCC5171/5181/etc. neckband adapters that have been out for several months now, and they're only $50-80, so worth a try, but they will probably have more static/etc. issues though.

TWS earbuds, Bluetooth latency, old school earphones/earbuds, TWS adapters, dongles, et cetera: https://www.reddit.com/r/HeadphoneAdvice/comments/13dkrif/earbud_upgrade_apple_airpods_style_low_latency/jjkzzgy/ and https://www.reddit.com/r/headphones/comments/13pwcev/would_you_spend_1k_on_tws/jlbw0sd/

Here's more info on TWS adapters like the FiiO UTWS3/5, KZ AZ09 Pro, etc. alongside adapters/converters, AptX Adaptive dongles (KB9P, YET-T10P, etc.), and so on needed for them: https://www.reddit.com/r/headphones/comments/11xmti7/unpopular_opinion_i_do_not_enjoy_qudelix_5k/jllhw46/ and https://www.reddit.com/r/HeadphoneAdvice/comments/13sbx39/aptx_vs_aac_on_mac/jlp72pk/

More info on the TRN BT20XS TWS adapter: https://www.reddit.com/r/inearfidelity/comments/17y3uj3/truthear_hexa_trn_bt20xs/k9vdy58/