skinny guy wanting to gain weight for muscle mass

Why have you stopped lifting? If you stop lifting, the weight you gain will be fat. You can dial back the cardio, but keep lifting heavy. Search bodybuilding.com for hypertrophy routines or articles on bulking. If you're having honest to goodness problems eating enough to bulk (eating at about 20% over your maintenance requirements), then perhaps look into adding in a protein shake or bar to get more calories in. Make sure you're eating full fat dairy and no reduced fat versions of most things. But, most importantly if you want to gain muscle, you must lift heavy. I don't know anything about working around acid reflux or the dash diet, but perhaps breaking your food up into 6 400 calorie meals/snacks a day will help.

I can't offer any expertise here, but I am curious about the responses you'll get.

I suspect you should:

-eat at a slight surplus (10%?--that's a guess)
-significantly increase your protein intake. I haven't looked at your diary; i'm just making an intuitive leap based on what I read.
-continue lifting heavy.

My husband is exactly the same way. He's 6'4" and weighs 166-167 in the mornings. That's the heaviest he's ever been. I swear his bones are made of feathers because he has quite broad shoulders, but a 32 in. waist (but he'd love if they made 33s lol). He gets acid reflux easily (finally went to the Dr about it).

Anyway, he lifts weights and swims a few times/week and it has made a difference in his physique. He's gained about 10-12 pounds in the past few years (yes, years). I notice that when he doesn't work out, he loses muscle quickly. He stays skinny though. It's just his body type. He has a hard time gaining weight and eating a surplus. He needs 3000 or more calories/day to maintain his weight (we've tracked) and he could kinda care less about food most of the time, so it's a struggle. What has helped is eating more home cooked meals (better ingredients,way more veggies/fruits, organic meats), waaaaaay less fast food (he used to eat it everyday), and adding protein bars as a snack before workouts. He also uses "Dark Matter" after his workouts. Those were the "small" changes he could make so far.

So, my advice is keep working out. You will build muscle, you just probably won't get bulky, just lean - and that's great! Stick with it.

Simply eat more. No magic to it.

I'm 6' 2" and 250lb + and its by eating LOTS.

Calorie bulking intake is 6500 and cutting is 4000. I need lots to grow. No more complicated than that - he's simply NOT eating enough.

http://iifym.com/tdee-calculator/

is another calculator.
lift in a range of 8-12 reps, hit every body part, mix compound isolation. try to do cables/freeweights.

if you are new to lifting go for a higher rep range to prevent any injury for your auxiliary muscles due to them being "weak"

Note: I stopped all exercise as sort of an experiment here to see if I can gain weight by eating as much healthy food as I possibly can. Yes.... good point, I will increase my protein input and try to drink more protein shakes.

Suppose the above experiment works. You reduce energy output as much as possible to try and create a surplus. How much of that weight gain do you suppose will be muscle in the absence of resistance exercise?

I'll give you a hint: Not a good idea unless your goal is a belly-bulk.

I would suggest you look for calorie dense foods (aim for about 10% above TDEE in total), do little to no cardio and lift 3 days per week on a full body program that uses progressive loading.