With Monero, there's no need to coinjoin or any of that crap, but it's lacking in the multisig department. There's a workaround though if you want some real anonimity, but you still want to use BTC.
- Open up an account on any exchange (from here on out, referred to as EX#1) that offers XMR, with your real info.
- Open up an account on any exchange (from here on out, referred to as EX#2) that offers XMR, with fake info.
- Send USD or BTC to EX#1 with your real info to buy XMR.
- Withdraw the XMR to any address you control.
- Send the XMR from that address to EX#2.
- Use that XMR to buy BTC.
- Send that BTC to your DNM of choice.
- Buy teh drugz.
If you're able to buy BTC anonymously through channels like LibertyX or you're lucky enough to have access to a BTC ATM that DOESN'T require ID, then skip to step 7 because this tutorial is redundant for you.
Why not just buy with real info, send to Monero GUI wallet, and then DNM? Doing what you said would have transaction fees as well as two exchange fees. Would effect the small buyers heavily and they are over half of the DNM purchases. Bigger buyers don't really use the markets, as far as I know.
Also, whats the point of buying XMR if you're just going to buy bitcoin with them? Public Wif i> LocalBitcoins > Cash Deposit > Send Electrum > Send DNM. Easy as pie my guy.