It sounds like what you need is a front end for your recording. That means: mic(s), preamp, converter, soundcard/interface. So that's what I would suggest you focus on, and you can certainly get a great sounding front end for $4,000.
You might consider adding another mic or two. Kind of hard to know what to recommend, but you should definitely check out some mics to add to the 414.
Preamps. You need a great preamp. There's some excellent preamps by Great River, Grace (201), Pendulum Audio, Millennia Media (HV-3b or
HV-3c), John Hardy, the list goes on and on. Basically, plan on spending about a $1,000 per channel and you'll be in the ball park as far as budgeting.
Conversion. The importance of high quality conversion can't be overestimated. So take a look at
the Apogee Rosetta 200,
UA 2192, Lavry Blue series, and maybe a few other 2 channel converters. A lower priced entry would be the Lucid 2496. But I think you can fit one of the pricier ones into your budget.
If your current soundcard has SPDIF or AES inputs, then you probably don't need to upgrade that. But if it doesn't, then you should get a professional grade interface for your PC. The M-Box works well, although I do prefer the Digi 002R. There are aton of interfaces out there, so just get what works with your software.
So really, that's my opinion of how you can spend $4,000. You can make first class choices and still get everything you need. Congratulations!