Magus Melt functions as a modded bonus rather than a conversion, so it's a straight damage upgrade. I also run Eternal Logistics so I get better sustained DPS.

Lockdown and repair. They're both just too good, even with lockdown nerfs it's a really good arcane for last grasp to CC normal enemies and get free headshots to revive yourself. I could replace lockdown, but idk what to even replace it with since most stuff isn't that good looking. If dissipate wasn't such a nerfed arcane I'd probably pick that.

Magus Vigor & Lockdown for operator, virtuous strike & shadow for amp

I equipped magus lockdown and magus repair years ago and I'm still using them. Lockdown is great for general objectives or harder enemies and repair is invaluable if playing a warframe with no self healing.

I was thinking of replacing lockdown with something else since it's pretty circumstantial but haven't really seen anything that caught my eye (while being easy to farm).

As mentioned already, magus melt will definitely be an upgrade (210% increase to total damage).

If you are using specifically klamora, I'd consider swapping Virtuos strike for Eternal Logistics, as it will add 70% total up time. That's 70% more damage per mag.

In comparison, your Virtuos strike with 7x7 amp will add an average 63% damage while active. 58% damage if your using 7x3. (using the dmg * (1+cc * (cd -1)) = avg dmg equation)

Although it's up to you if you want higher burst damage

Also btw if you're in the Zariman, Raplak prism has more dps against void angels and thrax if you have good headshot aim due to klamora having a wide angle making headshots difficult (and pairs well with virtuos shadow rather than logistics) though I would recommend klamora instead in the Undercroft.

Melt and Replenish on Operator, Eradicate and Logistics on amp.

Amp is a 743 or 747, can't remember which.

I run Unairu unless I know I'll be running a strip frame.

If loadouts were better, I'd probably have other options setup.

elevate and melt or elevate and lockdown or elevate and cadence, if I played more pubs I'd probably run repair since elevate sucks as client
eternal eradicate and onslaught, I don't see a point of using any other ones in general gameplay

My setup for context: Operator: Magus Anomaly & Magus Lockdown Amp: Eternal Eradicate & Eternal Logistics.

Anomaly and Lockdown give light grouping and CC to all frames, at all times, regardless of energy constraints. They open the game up in a completely different way and I don't think I will ever switch off of them with the exception of Magus Elevate for things like eidolon hunts and profit taker where CC is irrelevant.

The Eternal combo gives you more than enough damage to kill things, and unlike a lot of the old arcanes they're not percentage based activations. Dump your energy bar, get a huge power spike on demand, always when you want it, always within your control. Combined with Unairu or Madurai, even with Zenurik's AoE slow to a point, that's more than enough damage to take out enemies even well into the steel path. If you're running armor strip or unairu then you will always be able to kill with the operator.

Magus Melt is unique among the operator damage arcanes. Things like Virtuos Trojan and Forge convert damage into their respective types. Magus Melt works like a heat mod for your arcanes, giving you additional bonus damage on top of your void damage, without taking anything away. It's viable because of that, but I just don't find I need that level of firepower enough to give up Anomaly and Lockdown.

When I'm expecting my Operator to be capable on their own and do some heavy lifting, this is my setup:

Magus Lockdown is just a super useful CC. I'm generally in situations where no amount of extra health/armour is going to stop the Operator getting oneshot, so the natural shield gate plus Emergence Savior gives me a guaranteed 6 or so seconds to get done whatever it is I need to get done

In less intense content, I'll sometimes swap out Savior for Magus Elevate so that I have some on-demand Warframe healing, but generally any Warframes that are health/armour tanks already have their own methods of healing, and it won't make much difference to the shield gating ones

Eternal Eradicate and Eternal Onslaught give me the best damage buff to my amp, and I'm confident proccing both with any of the focus schools and their abilities. I typically run the 147 (Raplak, Phahd, Certus) amp in general gameplay so I'm looking to do burst damage, rather than longer sustained damage from something like the 7 (Klamora) prism, where Eternal Logistics or Magus Melt might be preferred

Returning to the game and noticing our much Focus I can get from Thrax

Also, don't underestimate putting lenses on your gear. If you put r3/4 lenses in your frames you know you gain a lot of xp with, you'll get tons of focus. Adding them to your best weapons is always a good idea.

If you can't do 3/4s, put whatever you can on, it's better than nothing, and you will end up with a lot of focus over time.

I've been running these arcanes for a bit now. The energy from Emergence Dissipate has helped me remove my dependency on Zenurik and allowed more use for Vazarin, Madurai, & Unairu.

Magus Repair for the ability to heal all nearby frames is nice, then Eternal Eradicate & Virtuos Strike for greatly increased damage.

Like others have said, Magus Lockdown is also super useful if you don't need the energy