Is Dina D'Malchusa a din in Gavra or in Cheftza?

Question

Let's say that Reuvain owes Shimon money in American law, and Dina Demalchusa applies, does that mean:

1. Reuvein has a halachic monetary obligation to Shimon which is as strong as any other obligation, and Shimon can take him to Beis Din over it, or merely
2. Reuvein has a law between him and Hashem that he must pay Shimon?

Also, assuming that Reuven and Shimon both pass away, with Reuven "owing" Shimon money, and his inheritors are in another country who don't follow that "rule" entitling Shimon with that money:

1. Must Reuven's yorshim pay Shimon's yorshim (inheritors), as it became a classic hischayvus (monetary obligation), or
2. Is he free, as the obligation was on Reuven and not on his money (somewhat similar to the case of a knas (fine))?

Answer 1

I haven't had time to go through the whole sugya, but this article by Dov Daniel (published in Daf Kesher vol 922, Parshat Pinchas 5763) seems to say that it is a din on the gavra and not the cheftza:

דברי ר' יונה:

"לא הוזכר דינא דמלכותא אלא בהפקעה שהנכסים מופקעים מבעליהם בדיני המלך וכענין הפקר בית דין הפקר ומי שיורד בהם במצות המלך זוכה בחזקה אבל כל זמן שלא החזיק בהם לא זכה בהם"
([Commentary to] :ב"ב נד)

מכאן שאין המלכות יכולה ליצור חיובים אלא להפקיע בעלות ואפילו אז, ההפקעה רק מאפשרת לתפוס אך אין היא חלה עד שייעשה מעשה קניין. כלומר, "דינא דמלכותא דינא" היא קביעה שמתייחסת ל"גברא" - התורה מכירה בזכות המלכות לעשות מה שרואה לנכון אפילו בדיני ממונות אך רק במידה שהיא יכולה להתיר מעשים של השתלטות ולא במידה שיכולה לקבוע קביעות שיתפשו בעולם של חושן משפט, כלומר אין המלכות יכולה לפעול ישירות על מעמד ה"חפצא".

In short, it would seem that the goverment has the halachic standing to confiscate Reuvein's money, but not to directly assign it to Shimon. Shimon must go and be koneh the money in order to acquire it. Much the same as when Beis Din is mafkir someone's property.

I'm going to keep looking into this.

Answer 2

Nedarim 28a (http://hebrewbooks.org/shas.aspx?mesechta=16&daf=28&format=pdf) states that it is forbidden to lie to avoid paying tax because of Dina DeMalchusa.

The Ran there implies that it is ( or at least could be) talking about where the right to claim tax was sold to another individual*, and that obligation to pay is still governed by DDD.

If it's just an mitzva of some sort it's hard to see how the right to claim could be sold to another person, and still exist as a genuine obligation to that new person "governed" (heh...) by DDD. This would then point to it being a regular debt to the King/Government like any other, which can then be sold by them to individuals, like any asset.

(Something like "tax farming." See https://en.wikipedia.org/wiki/Farm_(revenue_leasing)#Historical_use)